Zoro has done jack shit that would identify him as a traditionally bad pirate, much like Luffy. They do not rape, pillage, and or extort innocent civilians out of their money. The only reason both are even considered Pirates is that they sail the seas without governmental permission/fight against the government. Something tells me that if anybody in Zoros family that disliked pirates heard what kind of "pirate" Zoro was they would be more than okay with it.