That seems like a rather fragile distinction to draw. Tor isn't just a software stack and protocol. It's also a service made up of many hundreds of volunteers

That seems like a rather fragile distinction to draw. Tor isn't just a software stack and protocol. It's also a service made up of many hundreds of volunteers who agree to relay traffic, blindly, anywhere, despite (a) knowing what kind of traffic they're protecting and (b) having the ability to blacklist destinations. For instance it's common for Tor exits to ban SMTP or Bittorrent ports. Bear in mind Tor also supports hidden services, and could also choose to blacklist them if they want - the way the protocol works does allow that, and of course they could change the software stack and the nodes listed in their directory services to make such things easier. So Gab is a service run by a bunch of people that allow stuff pretty liberally, including bad stuff. So is Tor.