Sure he has a crew and a ship, but he hasn't done any pirate like things. He hasn't killed, raped or plundered anything. He's more of a vigilante/troublemaker.
He doesn't even mess with the locals, he actually does the opposite and helps them most of the time. He isn't the slightest bit interested in any of the wenches, even when they want him. For most part, his fights are in self defense and even then no one really dies.
Sure he messes with the marines/government, but any random person can do that. Doesn't really make him a pirate. His dad does that too, but he's labeled a revolutionary instead of a pirate. Pretty sure he has a crew and a ship too when he needs to travel.
Some of you might say, "it wouldn't be Luffy if he did any of that". But that's exactly why he isn't a pirate. I doubt Roger meant a future for pirates where kids just romp around in the ocean for fun.
Would Luffy be labeled a pirate in our world? No probably not. Is he a pirate in the OP universe? Most definitely. Anyone who raises a Jolly roger is considered a pirate.
As described in Romance Dawn there are 2 types of pirates in the world of OP:
Peace Main: Pirates who became Pirate for the adventures and not for personal greed.
Morgania: Pirates who became pirate for personal greed. Be it treasure or causing misery to other people.
Luffy and his crew attempted to plunder in sky island if I recall. Of course, that cost them a huge pillar of gold which the skylanders which about to gift them right before the strawhats escaped with negligible amounts of gold which the skylanders did not value at all. That said, luffy is a textbook pirate according to OP rules. He does not follow any particular law from any government and has a jolly roger. That is more than enough for him to be 100% pirate.
Like all all other pirates in OP(except some)they set out to the sea in search of OP.But Luffy has a somewhat different "agenda"then most pirates.He set out to the sea looking for OP,to become the pirate king AND adventures.(That explains why he stopped Rayleigh from telling them if OP existed or Raftel)
Throughout the series,the moment Luffy smells an adventure somewhere,he"ll definitely go there no matter how dangerous it is.
And due to his kindheartedness,in his adventures,he"ll help out those who are in need of help no matter who the person is.Thats why he defeated Croco in alabasta.
If you noticed what causes his bounty raise.Its because of helping others.
Yes, Luffy is counted as a pirate. He counteracts and defys the government, and although it is corrupt, still counts u as an outlaw, and he still takes pleasure in wine, adventures, the jolly roger flag and a ship, slightly treasure, the sea etc. He is more like a powerful sailor that is desperate to save his nakama, but nevertheless, he is a pirate, a peace main as smit says
Well, he is not really a pirate. He is THE Pirate King !
I say Luffy is a pirate, a good pirate, but none-the-less a pirate.