The only reason I could see to fire him would be based on a couple of grounds...

The fact that his public actions have demonstrated his lack of judgment. He is a prosecuting attorney, so any case he works on will be under extra scrutiny and could be up for appeal. If he works on a case that convicts someone, they could appeal it based on his demonstrated poor judgment and obvious bias that leads him to extreme actions. Imagine if he worked on a case that was to convict a gay person of some crime. His actions open the office, and the state, up to more expense and a greater burden, and even if he is assigned to cases where his expressed bias won't have an affect, that means he is permanently limiting the work he can do.

But, if they fire him for any other reason, then it would be wrong. Very wrong.