Your attempt to compare professors who are there to teach the curriculum of the specific class to a preacher who is there to teach the word of God is lame at best.

People are required to pay money in order to get the credits required to graduate with a degree.  People go to church voluntarily to hear a preacher teach the word of God. They are free to leave at any time and there are no repercussions for doing so.

But then again... I think you knew that.  You just wanted to try to take a cheap shot at Christians.