Eventually, we will work alongside them on multiple colonies, after they've made the bed for us.

I wonder about this. If we try to put a date on it, optimistically, we are at least 15 years out. Realistically, it's 25 or more. It is reasonable to assume that AI will be so improved over that time, that robots will not only be almost as mentally flexible as humans (if not more so), but physically they will be leaps and bounds ahead.

At that point, I think we are left with the question: Why are we going to Mars?

If it is only to explore and understand Mars, then it is likely that we needn't ever set foot there to accomplish those goals. However, if the reason is 'to be there', or 'to spread our species across multiple planets', then I can see it happening. Perhaps more likely, the reason will be 'to get there before X country does'.

At any rate, I don't believe that a one-way trip is immoral if it is to accomplish the first two of those objectives. Unfortunately, the third objective is the one that would be more likely to make it happen.

As an aside, since Mars has 1/3 the gravitational pull, the machinery required to build underground bunkers might not need to be that heavy. Soldiers built bomb-resistant shelters in WWI by hand. My father often had to dig two foxholes in one evening in Vietnam. Given a few days, a few people might be able to make an impressive bunker with dirt that is so much lighter, and any ceiling materials could hold that much more. I think I read that about 2 meters of dirt would provide adequate protection. You could start at a bluff, fill sandbags, etc.