“Basically, I think it’s a mistake to share a public platform like this with Creationists. Unless they can be questioned directly, it is simply a forum to make equal speeches in equal time. And that gives Creationism legitimacy.”

I agree completely.

A related problem with a “debate” like creationism / evolution, or astrology / astronomy, is that there’s a lie that permeates the entire affair. The lie is: “Here we are searching for truth, open to new ideas, working together to improve our knowledge.”

I’m basically saying the same thing that you are, but I think it’s this particular lie that lends legitimacy to creationism. The first step is to remove the lie - i.e., don’t hold a “debate”! The point is that changing the rules, e.g. allowing direct questions, does no good, because the whole thing is based on a lie.