@SteveBologna absolutely.

The problem is they will say "I didn't know he was going to commit murder when I sold the gun, but I know the gay couple will commit gay marriage with my cake!"

But what if a guy orders a cake and there's no rainbows or names on the cake but you stalk the purchaser on Facebook and discover it's a gay wedding, then refuse to make the cake.

So why wouldn't you insist on background checks before selling anyone a gun instead of claiming ignorance and innocence?