why are people so up in arms?

He most certainly has the right to sell it. In my opinion, he could hardly have picked a more disgusting thing to do at this point in his life, but he does have the right to so.

Rather than the question of Zimmerman selling it, I'm more concerned over what kind of person would BUY something like that. Zimmerman wants some money, that's easy to understand; it's a bit harder to understand why someone would want to own a murder weapon that one stranger used to kill another stranger.