Just because a site is developed by a non muslim doesn't make it a bad site. Yes, as muslims we should be aware of their intentions, misinterpretations, misquotes etc.
I've been surfing many of those sites for more than 5 yrs now. I must admit, my understanding of some aspects of my religion is way better now. Alternative views from these sites opened up my eyes to look for better answers and to free up my mind from blindly believing something to logically believing it.
It was a great way to know the other side of the faith which only helped my faith to grow stronger.
I know, it might not help everybody the way it helped me, so I'd say use your head.