Centrism is, by definition, fence sitting. Someone who is a centrist will often reach a conclusion along the lines of "the left is too extreme, the right is too extreme, therefore whatever is halfway between them must be right."

This obviously causes some problems. Someone on the left might say gay people are human beings who deserve dignity and respect, while someone on the right might say gay people are icky and unnatural and shouldn't exist. A centrist would naturally conclude that both positions are too extreme, so how about we treat gay people with dignity as long as they stay in the closet and pretend they aren't gay? Then everyone's happy!

Centrists are like libertarians. Their ideology sounds really enlightened and appealing, but in practice, it usually ends up screwing over a lot of people, especially the most vulnerable, and benefiting social conservatives and the wealthy.