That's sort of what I'm thinking. Dogs frequently kill livestock, and kill many more people each year than mountain lions. I'm not sure that gives me license to kill every dog I see under the guise of protecting myself and my property. Same with deer- they cost farmers plenty, and have been known to attack folks. That doesn't mean I get to shoot every deer I see on sight.
There's no evidence the animal was threatening people or livestock, and if it was, there are better ways of dealing with it (call the agent, at least that way it's on the up-and-up.) This guy instead chose to kill a protected species- that's a crime, and IMO he ought to be treated like any other poacher.