They think its justifiable because to them they weren't bad rats. For example providing information to the feds for other mob guys in other families and never giving information out to the FEDS that would hurt their own family or crew.

For example say a crew in the Gambino Crime family was trying to take over the Garment district that the Lucchesse crime family was running. Well I could simply just cut a deal with the FEDS where they would take down that crew as long as I gave them information on what they were doing.