I've said it before and I'll say it again: the "if we teach Biblical creationism then we have to teach all the other religions' creation myths too" argument is a bad one to use against these loons. They're not interested in "religious freedom" or "equal time" or anything else of the sort; what they want is a Christian (specifically fundamentalist evangelical Protestant) theocracy, and no one should have any illusions about their goals. If they get their way, we will have to teach (their version of) Biblical creationism, and we will not have to, or even be allowed to, teach anything else.
The same goes for the closely related "if we have Christian prayers in schools, then we also have to have Jewish / Muslim / Buddhist / Hindu / Wiccan / Satanist / etc. prayers too" idea. This is an appealing argument to tolerant, open-minded liberals, but it is a dangerous misunderstanding of the thinking of the religious Right.