Yes, but that may work out. This attack may provoke him into Open War, draw him out into the open where it's clear the everyone what he's doing. It'll be easier for the other Gangsters to fight him that way.
EDIT: Forgot that Rosetti works for the leader of the Soon-to-be-Mafia. That makes things a lot bigger than expected. Unless they convince the Boss that Rosetti is too unstable to keep around.