Back then we were all nuclear 'activists' to some degree.
He became a hero when he became a free speech activist by creating and releasing PGP (and then facing retribution from the DoD and DoJ). Without that conviction we may not have any person to person encryption now.
FYI: even a few cypherpunks were unwilling to take those same risks. Most of us made our opinions clear by publishing our public key on the mailing list. 

 Wow, so you're like a real OG.😲


What was the nuclear activism about?

Were they protesting to stop the production of nuclear weapons? Were they being surveilled for this activity? 
 

 I'm ancient. I go back to the (surveilled btw) vietnam demos. '69 or so.

Yes. Nuclear weapons...I don't recall fear of nuclear power (e.g.) except by some general association with weapons.
I don't recall anything specifically about PZ as a nuclear weapons prolification activist except the general statement that everyone was opposed to it. I would think I would have heard (and remember!) if he was unusually activist in that area tho. 

 Thanks. I've always been curious about it. People were against nukes in the 80’s, but nobody seems to mind now.   

 fyi: i was wrong it seems. Phil was actually jailed a couple of times for his activism. Strange i didn't remember that - maybe i never knew! 

 Activism was so hot in the 90s 

 My best friend's dad was an old hippy and nuclear activist in the 80's. I thought it was interesting, but it appears that chapter of history is over.