>Some of the people given 30 weren't even at the protest.

That by itself isn't a convincing argument. You can't plan a bank heist and be waiting at your safe house and say, "I'm not guilty of anything, because I wasn't in the bank!". The mafia guy doesn't get to say, "I didn't actually whack the victim, I just nodded to Joey, and he did the whacking".

You might be interested in:

https://en.wikipedia.org/wiki/Criminal_conspiracy

...maybe this is mostly a thing in common law jurisdictions? Maybe there is a lawyer here who can point us to a interesting history of conspiracy in common law vs civil law jurisdictions? Also of interest might be things like:

https://www.justia.com/criminal/offenses/homicide/felony-mur...