(Calling a person immature because you disagree with their opinion is an ad hominem.) Does this strike you as ironic? Speculating on the maturity of someone you/others don't know, perhaps? 1 opinion does not define a person. Certainly not me, at least.
Surely, I support any "dealer's" choice to refuse business to anyone for any reason. That's a free market. It's simply irrelevant to this particular discussion, and while I'm sure I'll end up unscathed, could potentially harm one's reputation simply by suggestion (despite, again, being irrelevant to this topic).
I'm not going to question anyone's business integrity because they worship Jesus, for example, and I do not. It's irrelevant to said practice (unless they're putting stickers of Jesus on comic books/slabs - but that's not an indictment on the practice).