Because most of the Christians on this site present themselves to be those hateful bigoted ones. Either that or they refuse to listen to anyone else's viewpoint and misrepresent others beliefs. Or both. We shouldn't assume you are all like that, true. But, it is hard when that is most of what we see on here.
And it's not just on here either. Prop 8 in California, Bush attacking Iraq because God told him to, etc... These major things effect everyone. We are supposed to be a secular country, yet, it seems, the far-right Christianity base will stop at nothing to change that. And if they aren't the people directly responsible for the erosion of our secular government, they are voting the people into power who are. I'm sorry, but I don't want my country to be another theocracy like Iran or Afghanistan flying a Christian banner instead of an Islamic one.
If you aren't like that, bravo. We'd probably get along fine. I have no problems with any religion in general. I simply have problems with religious people who feel they are above the law and can do whatever they want, yet then hide behind it and cry foul the second the tables turn even slightly.
If they would calm down, I'm sure they would be more than surprised to see how much the rest of us do as well. They encourage the opposition and dislike you speak of in your question.
Edit: May I please point to Lightening from the East and Marz SFECU's answers? These are the people who are making you look bad. I'm also going to go ahead and cite Camille as well.
These answerers have reminded me of another reason. A complete lack of responsibilty for one's own actions. (Not all Christians again to be clear) You ask an honest why question, Camille gives you a "we're supposed to be hated. It means we're doing God's work". Complete lack of ability to look at her own actions for even 5 seconds. That verse sums it up for her, and that's it. Case closed.