I could probably set up an interesting RP about activism. There is a lot of inter-character drama that will bloom so very easily with the subject, you just need to set the scenarios and bring in characters with a common goal but a different means to achieve it. Also you can throw in adventure, like stealing a ship to block a trade route or invading a facility to interrupt a speech.

As for your example... It's totally fine for a character to have the baby seals on their mind. I mean let's be honest here, not everyone is going to like everyone's characters. I know I've played with a couple people whose characters I wanted to hit over the head with a brick. But you know why I didn't tell people to change their characters? It's because I don't get to decide other people's characters for them. Your characters can get pissed, dump the Greenpeace freak for the mission or lock them up for jeopardising the operation, etc.There is that option for repercussions, sure, but you can't tell the players "Your character can get angry at X but not at Y because I want your character to act like Z."

tl;dr Stop being such a narrow-minded jerk. It's becoming a recurring theme with you.