Yes, there may be lots of people who REALLY wanted a place and didn't get an offer, but my point is that if you did happen to get an offer, that wouldn't mean you'd somehow be morally obliged to accept it just because there are other people who wanted it. You have no way of knowing why those people weren't given offers, and there's no guarantee that if you hadn't applied one of them would have got your offer. For all you know, your college may have decided to do with one fewer theologian than usual that year (or conversely, they may have been so impressed by your application they decided to give out an extra offer which they wouldn't have given to anybody else).
As for the "making their lives a little bit worse" bit: don't get me wrong, I do believe in altruism, but I also believe that when you're making a decision about where you
are going to spend the next three or four years, that's not the right time and place for it. It wasn't your decision to give you an offer and reject the other applicants, it was the faculty's/college's, and as I said before, you have no way of knowing how they arrived at that decision. There is no guarantee that if it wasn't for you, it would have been they who got the offer. You're not personally responsible for the fact that those people are feeling miserable about their rejections, and you're not going to make them feel any better about it by accepting an offer you don't really want to accept and potentially making yourself miserable - and it won't get them a place either.
I'm not saying that feelings of guilt/responsibility wouldn't be understandable in this situation, but nevertheless I think they'd be misguided.
Besides, as The_Lonely_Goatherd pointed out, if you turn down your place, it means that someone who narrowly missed his offer will be given a place anyway, so the place isn't actually "wasted".
No, it's not. Your offer is given to you by your college, not by your rejected fellow applicants.