Libertarians don't agree that the inability to protect the environment makes their philosophy invalid either. The fact is though, most people look for reciprocatity in their moral philosophy.

It's not that every individual has to agree not to kill you. It's that we have to agree that punishment is appropriate for killers. Getting specific - it's incoherent to say it's immoral for humans to kill rabbits but moral for foxes to kill rabbits. To have a consistent moral philosophy, you have to either punish the foxes and try to prevent them from killing the rabbits, or you have to admit that killing rabbits isn't _really_ a problem.

I'm not arguing that it's moral for foxes to kill rabbits. I'm arguing that the presence of immoral actors does not negate the arguments in favor of morality. Foxes aren't immoral, they're amoral. It's wrong for me to kill people even if natural disasters do. I can't have a moral discussion with a fox.

It still doesn't follow. It's wrong to kill because of the harm killing causes. Whether the killing is done my an immoral or amoral agent doesn't change the effect. If you really believe dead rabbits is a bad result, you ought be spending your time preventing the amoral agents from causing that bad result.

Consider an infant - an infant is basically an amoral agent - it doesn't understand killing. If a infant kills somebody with a gun, we don't say "oh well, he doesn't understand killing" - we say "why the heck did that baby have a gun? Where are his parents?" We expect moral agents to prevent amoral agents from causing harm. So why aren't you trying to prevent the foxes from killing the rabbits?

Am I obligated to personally intervene in every bad thing that happens in the world as a prerequisite for pointing out they're bad? Your argument seems to boil down to "you aren't trying to stop all instances of a category of bad thing, so your opposition to that category of bad thing is invalid", which is a pretty weird argument. I also think murder is wrong, but aside from personally not murdering, I don't do anything about murders happening in the world.

If foxes are amoral agents, why is it immoral to kill them?