Dude, take your meds…well, yes, you see what Popplers turn into? Hedgerow I take it you are cultured enough to be familiar with Futurama?
It doesn't have to be a cruel, violent, malicious act. It could be as simple as placing them, collectively, in a chamber. A chamber in which helium is fed in, and oxygen is not. They would simply go to sleep and we'd rid ourselves of the problem.