I don't think we, as a society should limit what we allow directors to attempt to do an not do. If someone feels they are ready to create a horror film, we should be more than supportive of their decision. What is the worst that could happen? The movie would bomb and they would learn a lesson. Let's allow directors to do what they feel they are ready to do, and nothing more.
Yes, comedy directors should have the chance to direct horror films. I believe this for three reasons. First, films are films and every director should have the opportunity to create quality movies. Second, I believe that directors should be able to test their skill boundaries, meaning that they should be able to experiment with film. In essence, they should be able to take every advantage to build their portfolios. Lastly, the comedy director can lend a horror film humor at the right time lessening some of the tension.
Directing is the art of handling a script and the individual talents and personalities of a cast. Producing is a totally different animal. Some directors can do both, but that doesn't mean that everyone else can or should even be allowed to try. Also, comedy and horror are different genres for a reason; most people who are good at one cannot do the other. To assume a comic director is a natural talent at horror is very foolish.
The problem with this question is that it assumes that other comedy directors are as funny as Mel Brooks. They are not. Also, producing a movie is not the same as directing a movie. There are some vast differences in the roles that each profession plays in the development of the movie.