And a K-Mart salesperson does not have the right to refuse to sell you ammunition to prevent you from killing someone?
"Billy Cowart and Julie Elaine Cowart, individually and as representatives of the Estate of Richard Glenn Cowart, Deceased (collectively, the Cowarts), sued Kmart Corporation (Kmart) for negligently selling ammunition to Manuel Carrasco and James Gabriel that another person, Leonard Bell, used to shoot and kill Richard Cowart."
-- Cowart v. Kmart Corp., ___ S.W.3d ___ (Tex.App.-Dallas [5th Dist.] 2000)
The old, "Damned if you do and damned if you don't", huh?
If K-Mart knew you would use the ammo to go murder someone, then they have a moral duty not to sell it to you. However, they should not be legally prevented from doing so nor should they be held liable if you go kill your wife.
It's only because of guys like John Edwards that a company can be sued for selling a legal product that is later used illegally.