Evangelical and Fundamentalist Christians, specifically are, in my opinion, dangerous if mixed with politics or other arenas where they are granted social power. The reasons for this are quite obvious. [edited to add: I don't think religion should ever be mixed with politics, but some seem more dangerous to me than others. Evangelical Christianity is one of them.]
In the first place, they believe in a worldview that contains absolute good and absolute evil, when clearly the world is not like that. Secondly, they believe in the End Times, which is more than a wee bit worrisome for those of us who don't wish to see nuclear bombs dropped all over the place in the name of god's will. Third, they have a one-size-fits-all mentality, which is probably why they are a strictly American phenomenon -- the US doesn't promote diversity in the same way that other Western nations do. Yours is a melting pot, with greater emphasis on uniformity. (Chances are good that you would have to spend significant time outside of the US to see this difference, since it is very subtle.) The surge in Evangelicals in the US is probably the result of the Age of Reason, where liberalism/individualism has been centre stage for 150 years. Fundies are collectivists and broadly resent individualism. (I recall reading a Rapture nutter saying she was taking her son out of public school because they were teaching self-esteem.)
At any rate, it is not Christianity in particular that is problematic. It is the idea of religion and politics mixing and sharing power. A cursory review of history should explain why that is.