The frown turns into a scowl as it doesn't escape his notice that the man isn't so much addressing him, but using this to preach his view to everyone else.

"Inaction can be just as bad. Are you going to just stand there and watch these people get slaughtered then?"

Anakin has the Jedi Code to follow so he disregards the warning. Maybe there was someone who might have benefited from the old man's words, but Anakin doesn't like that the man is automatically taking the moral high ground and seemingly looking down on everyone else.