I am pretty sure that their ruling bodies is not really the key difference. The difference is probably more like Aria said, and also on their methods.
The blood raiders spend their times farming the dark corners of space for fresh meat and blood. Their ships look like moving slaughterhouses.
The Cartel are mafia organized, offer people protection against their total submission (and their money, and maybe their families ?). They deal in crime in every Empire, drugs, murder, corruption, whatever.
The Guristas blow up people in space for money, the perfect archetype of pirates. They would sell their mothers for isk or just the pleasure to see the caldari megas burn.
Oh, I am pretty sure the Empires have their own dirty dealings either, but most of them are restricted by their laws (which make them look like hypocrites when it happens nevertheless). I do not see why it is such a problem.
Yes, I may have had issues repeatedly in the past because I was a little sad to only see respectable and noble pirates and wanted to see dirtier pirate factions. Whatever. It is normal to see most players trying to make their characters look good.