Yeah, I thought that was the whole lesson with Dale's killer and Carl not taking care of it. As is, Carol and Tyreese are being pretty selective about who they prevent from becoming a zombie.
They should have killed that guy by the train tracks if their logic is that they don't want to leave zombies as a threat. They're not entirely consistent there.
As an aside, that walker attacked Daryl and Beth because Carol and Tyreese didn't kill them. And Daryl and Beth got their revenge by sending them some burnt ones.