Resistance to ID is more a resistance to putting untestable, religious ideas into science than being opposed to religion (or Christianity) itself. ID only really works as a "negative" science - looking to poke holes in current theory that it disagrees with, and does not produce forward-looking hypotheses. It offers almost nothing in the way of discovery (what has ID ever done to help us unlock secrets of the universe?), and its only utility is to support the faith of those who believe that God did not or could not have created other than what they believe. And that utility is even limited because, by setting itself up as a matter of faith, when it proves wrong it hurts the faith of the one who believes in it.