I know this will take the argument into the different direction of "free market" etc. etc. etc.....
...But I rather not give my business to someone who will hang a "No Guns Allowed" sign up in favor of giving it instead to someone more likely to hang up a "Kiss My Glock" sign. 
BTW..... Right to refuse service to anyone? Tell that to all those race baiters at the NAACP and the Rainbow Push Coalition -- not to mention the gay and lesbian activists..... One of the most dangerous things any small business owner can do is refuse service to someone. If you do, then you are risking losing your entire company. They just are able to get away with it currently with gun owners because we dont bring frivolous lawsuits to further our agenda.
Try again. Its very hard to prove discrimanation. Now, yes they could boycot me, that is thier choice, I won't stop them from doing it.
The diffrence here is you have a choice on rather or not you have a gun, blacks are always blacks. Just like you have a choice to use my service or not.
I infact just turned down a remodel from a gay couple, the fact that they were gay had nothing to do with it. The fact that they were both lawyers and ones that are known for sueing over spilt milk was. The last thing I need is to be sued over a 1/16" mistake from the contract document, I've seen it happen. They can sue me all they want. I'll just add it to the stack of lawsuits I already have going and move on.( 1 dead beat client, and from the aftermath of a disapearing contractor)