More and more, I've run into atheists who support the Phelps family, not financially, politically, ethically, but to the extent we tend to support every religious view. And then some, truth be told, something refreshing about the Phelps family. Namely, honesty. There isn't an ounce of duplicity in anything they say, they say they believe the Bible and they do, they've read it cover to cover and believe everything therein. Their interpretations are, by and large, quite well grounded. I use to believe that perhaps they went a little too far and were going extra-biblical with their "God hate America" and "Thank God for IEDs" comments. However, after listening to the arguments behind them, I must admit that Noah's Ark and the destruction of Sodom and Gomorrah do at lend them a bit of leeway to make those arguments.
I'm not even sure that they are a hate group. Specifically they don't ever reference themselves. They only announce that "God hates Fags" and "God hates America" -- They never suggest anything of the sort themselves. They are non-violent and stay well within the confines of the law. Which is less than one can say about such great Christian establishments such as the KKK.
Other than cherrypicking there's nothing to attack the Phelps position with. That and the falseness of the Bible. The above video makes some guesses as to why some people might hate the Phelps so much, and I haven't anything better.
It also strikes a number of Christians as odd, that they believe America is doomed, and yet are wasting their time thanking God for bringing about this doom. Personally, I'm impressed by their resolve. They don't do it to convert people, they don't do it to save people, they don't even do it to warn people... they do it to thank and praise God for his judgment and primarily because the Bible tells them to do it.