But what if I put in my max bid, find out it's not enough, and then after some soul searching decide, "Well, OK, I'll go a little bit higher." I don't think I've ever actually done that -- but I would resent not having the option to do so.

I did that just recently, and ended up winning the auction. I didn't really want to go that high, but considering that the next lowest price I found on a similarly used item was nearly double what I won the auction for (and new ones are $1000+ over what I paid), I'm reasonably happy. So yes, I'd resent that, too.