Assuming for one second that there is a God, how can one be certain that the "mainstream" Christians have it right? How can one ascertain that Fred Phelps ISN'T actually talking to God? Because he's mean? I find a lot of religious teachings to be very mean spirited, but that's not the foundation of my disbelief.
It seems to me that once one takes the leap to believe in Christianity, all of the sects, including the extremists, have just as much likelyhood of teaching the correct ways of Jesus.