To some extent, yes. It really helps if you go back and look at the history of StarShip, from the very beginning. After SpaceX started getting the first stage of Falcon 9 back on a regular basis, they did look into trying to get the second stage back. Elon put out a number of tweets as they investigated what it would take. It turned out that the extra mass required for heat shields and propellant would have left it too heavy to carry a meaningful payload. So instead of continuing that line of R&D, they switched future planning over entirely to the reusable Mars Colonial Transport (which evolved on paper into StarShip). A large reusable Mars rocket of some sort had always been one of Elon’s goals; it just got sped up a bit because there was little point in continuing to evolve the Falcon/Merlin.

Now, could you build a reusable upper stage somewhere between the size of the F9 upper stage and StarShip? Sure, but if you have to design a clean-sheet rocket from scratch, you might as well make sure it can handle everything you want to use it for, and Elon wanted not just Martian exploration, but colonization.

This is a good point. It is best to leave only the minimum of final assemblies and connections as on-orbit activities. As we can see from what NASA charges for astronaut time on ISS, it is less expensive to do the most work as possible on the ground, before launch and the least assembly possible on orbit.
https://behindtheblack.com/behind-the-black/points-of-information/nasa-increases-iss-prices-to-commercial-customers-by-700/

One hour of crew member time, previously $17,500, is now $130,000.

With the HLS Lunar Lander contract, SpaceX has a paying customer for Starship.
After getting it into orbit, SpaceX will work on refueling. Lunar missions will need 2 or more refueling launches. Refueling missions for Mars missions will require 7 launches (1 payload, 6 fueling missions) for each vehicle going to Mars which is Elon’s goal.

If they put a full load of propellants in it for the test, then that weight will help to offset a few million pounds of that force. The hold-down clamps and the pad won’t necessarily have to handle the full force of all those Raptor engines.

Steve Richter,
You asked: “Is that why Starship has to be large? So that it can be reusable?”

Reusability is not dependent upon size. The two Dragon spacecraft designs, cargo and manned, and the Starliner spacecraft are all reusable despite their much smaller size. Since the Space Shuttle was likewise a large structure, I can see where your confusion comes from.

The space industry has believed that reusability is the key for reduced launch costs, with launch prices so low that many, many more companies, universities, countries, and individuals could afford to put payloads into space. For three decades the comparison has been to ask: what if we had to throw away every 747 that flew from coast to coast? The answer, of course, is that no one could afford to fly or send cargo by air. Reusability should make space access far more accessible to far more customers, and a quick turnaround time for the spacecraft and launch vehicle means that they are available for many launches per month. Or day.

The large size comes from the 100 ton capacity. It also comes from the desire to relaunch Starship from the surface of Mars back to Earth. Mars’s gravity is low enough that the Super Heavy is not necessary, but it is high enough that there is a delta-v requirement similar to getting from the point of separation with Super Heavy to low Earth orbit (LEO).

“If we do not need the liquid methane and oxygen, then is there a need for a large starship?”

SpaceX thinks it is desirable to take large amounts of payload and large numbers of people to Mars, so they chose a large spacecraft.

It isn’t just SpaceX that thinks a large launch vehicle is desirable. Congress required NASA to build SLS with similar launch capability, and years ago Blue Origin suggested that it would eventually build a similarly large launch vehicle, which many believe they intend to call “New Armstrong” for its capability to launch Apollo-mission sized payloads. Three different groups believe in a need for a large launch vehicle.

The basic idea is to reduce launch costs per pound (or kilogram) launched into space. Launching 100 tons into orbit takes about as many people as a smaller rocket launching 1 ton into space, so there is efficiency potential with the larger rocket for launching 100 1-ton payloads. The capability to put one large payload, such as a space station module, into orbit is also desirable. The space industry has longed for more variety of uses of space than our government agencies have delivered. Manufacturing is one area that has been badly neglected. Taking a large load of raw materials to a manufacturing space station may be desirable.

We on Earth could benefit from products manufactured in space, but government does not want to favor one company or industry over others, so manufacturing has been very low on their priority list. Space tourism is another industry that was difficult to get governments interested in. Russia broke the taboo when it needed money and started taking tourists to the Russian side of the ISS. Notice how few tourists went up while the U.S. was buying seats on Russian spacecraft, and notice that Russia is about to resume such flights — there is a planned Russian movie crew flight to the ISS, with the loss of Russia’s revenue from America.

NASA has rules about releasing scientific data that is generated on ISS. A commercial space station may not have the same requirement, so commercial space stations may be more desirable for many companies that want to do proprietary research in space.

Going to Mars in the next decade is a goal for SpaceX. The company believes that money can be made there and that there is no benefit to putting off the attempt. Building a Lunar base or station may benefit from heavy lift capability rather than smaller rockets, and we believe that water-ice exists at the Moon’s poles and can be used as fuel and oxidizer for space travel. It may seem counterintuitive, but it takes less energy to get propellants from the surface of the Moon to LEO than it is to take it up from the surface of the Earth. It may be useful to lift large quantities from the Moon to fuel interplanetary missions.

The beauty of having private companies doing business in space is that we get more results, and someone else — other than the taxpayer — pays for it. From the 1960s to about the year 2000, communications was virtually the only business being done in space, and most of it is still done by private investors. Ikonos was the first commercial Earth observation satellite, launched around the year 2000. The company Made In Space is already experimenting with manufacturing in space. Other companies have already begun to do other business in space. Not every launch needs to be 100 tons, but for those that have payloads that are less expensive to launch on Starship, it is likely to be there.

Starship is large and can move a lot of material so that a lot can be done sooner rather than later. If SpaceX is right about the profits that can be made at Mars, then moving a lot of people may be desirable. If not, then Starship will be more spacious for those who fly on her.

Quite frankly, the generations that watched the Apollo Moon landings were expecting so much business to take place in space that we thought that the movie 2001: A Space Odyssey was only a little bit optimistic. Little did we know that space exploration would be as hindered as it was. Back then, there was going to be a Space Shuttle making routine trips to space, there were plans for a space station, and we were already going to the Moon, so who would have thought that we would abandon the Moon for half a century or so, that we would let the space station’s orbit decay and wouldn’t replace it for another two decades (three if you consider its completion date as the replacement date), and that the Space Shuttle would turn out to be so expensive and fly so rarely?

It is four decades after learning of the degraded capabilities of the Shuttle and we now have hopes that we will have the inexpensive and frequent access to space that we thought would come from the Shuttle.. And it comes from We the People, who are finally going to get what we want, because government refuses to do it. (Who is our government working for?).

I actually do not know what I am talking about. Just thinking there is something off about launching the equivalent of the statue of liberty into orbit. And there are no informed, critical voices on the web or YouTube which are examining if the Starship approach is the best, most affordable way to get equipment on Mars.

If Starship is being built so large in order to transport people to Mars, I think that is nuts. People are not going to Mars in the next 20 years. Which is plenty of time to design and build the large craft needed for that purpose. And hopefully in that time we have new propulsion systems, some sort of solid, lightweight fuel. If we do not need the liquid methane and oxygen, then is there a need for a large starship?

Like so many other activists, they are consistently Progressives first, (insert stated cause here) second.

I think they should be getting some priority! Congress seems to assume SpaceX will pay for moon ships beyond the first flights, and the FAA / EPA are capable of shutting down Boca Chica, both things to please the left. And if Biden continues to crater, only the left will be there to offer any loyalty to the Democrats, so it looks like the left’s wishes could be running the show for a while.