"And how come no-one is taking trey Parker to tribunal, or running a social media campaign against him?"
Because everything South Park does is so over-the-top it's very obvious satire, which makes it hard (IMO) to take offence to anything they do.
Remember Isaac Hayes the voice of Chef? He rage-quitted South Park because they done an episode taking the piss out of Scientology. Which IMO was a bit hypocritical since Hayes was happy to pocket cheques for his work on South Park episodes which done other religions.
It does give some interesting perspectives on current topics time-to-time, but it really is just a cartoon for entertainment, that's all.