I would rather someone preach on their car in a non-violent manner, then have some Islamofacist "preach" total domination of the world by their violent religion. Here's a qoute from Omar Ahmad, Chairman Emeritus of CAIR (Council for American Islamic Relations), that "Islam isn't in America to be equal to any other faith, but to become dominant. The Koran, the Muslim book of scripture, should be the highest authority in America, and Islam the only accepted religion on Earth."
This guy wasn't harming anyone, and he wasn't in your face shouting Christ. He was displaying his love for his God. Why is that wrong? I wouldn't care. I don't mind any religion displayng their views, until they get in your face and target you. Then that's different. Better that than a suicide bomb for 72 virgins just because you are an American.