It's not the same.
Whitebeard: saying it's pointless to fight the Marines, since there will keep sending new forces anyways.
Greenbull: playing the tough guy, wanting to impress Akainu, yelling at the scabbards and saying he will kill thousands, because no one is allowed to disobey the WG. Yet when Shanks released some of his CoC from miles away, realizing that he has to run.