Another common reason that scientists or some people dont want to debate creationists is that they believe the case for evolution is settled. The view they hold is that the jury is in and evolution is true. With this statement I agree completely. But now with this in mind, lets extend this argument.
If you are not prepared to debate creationists, then why the hell are you debating theists? Seriously, the non existence of a god is as settled as the evolution case.There is no proof for god, just as their is no proof for creationism. However, we are prepared to debate theists for multiple reasons. One of these reasons is that maybe there is a god. But using this rational, creationism may be correct as well.
In closing, never be scared to debate stupidity. After all, its the only way to expose more people to the lies.