Way I see it, they're like the Vox populai. They started out peaceful, but due to no results they eventually turned. Those were the original syndicates.
Now, new groups of terrorists, bounty hunters, raiders, are popping up using the same name. Some of them work for other corps to bring down NT (Nuke mercs), some are there to do their own goal for a group (Traitors), and some are there because they're crazies, in a place among other crazies where they feel accepted.