Would you sell a gun to a guy who was going to rob a bank with it?
If not, why would you sell weapons or parts to a government agent, to use against citizens who aren't allowed those same weapons or parts?
I wouldn't knowingly sell a gun or accessories to somebody who I know has evil intent with them.
But all I'm doing is something that appears on all levels to be completely legal. Should I not go through with the sale to spite the guy because he happens to be a LEO that lives in CA? So he get's extra 'privileges' because he is a LEO - I don't see that as being a problem.