Why is he in a movie that requires him to handle a firearm? Seriously, one of two things: 1) Either his convictions about firearms are not that strong, which makes him a lying Hypocrite , or 2) He is a money grubbing whore. Personally I think it might be both.
Some of the most vehement liberals against firearms are actors that make insane money using firearms in an insane manner in insanely violent movies, just do a search on almost any 'action' star. Baldwin just added one more insane to the mix and it involves his brain.