Simply put, Amazon are the Wal-Mart of the Internet. Through economies of scale--as well as the fact that the management is heavily rewarded in the stock market for not making any profit--they are putting extreme pressure on small local businesses (as well as some other major players like Target, but I'm not shedding a tear for them), all the while subjecting their employees to slave-labor conditions.
They are like a weed, growing quickly and killing everything around them. I've got nothing against corporations that succeed, but I'd rather see Apple and Samsung battle it out and have one of them come on top (while we're all really rooting for HTC to make a scrappy come-back) than to watch Amazon killing the local bookstore, toy store, and other shops who simply can't compete. The long term effects of this sort of disruption are only now beginning to be felt, but it's going to get worse.
So in short, I despise Amazon because they are a massive juggernaut, destroying small economies and abusing their employees, and they do it by appealing to people's preference for short term benefits over long term investment. Me, I'd rather pay a couple of extra dollars and buy my kid's birthday present in a local shop from someone who will then spend the money locally than save a couple of bucks and basically water the weeds. What I fear is that there will one day come a time where the only place to buy a significant number of consumer items will be via Amazon.
I know that some degree of the same arguments could apply to a number of other large corporations, but for me, Amazon is one of the companies that is far enough over the line that, where possible, I try to avoid them completely.