Anyone heard of Colleen Patrick-Goudreau? She wrote a bunch of books about becoming vegan. She's an animal rights advocate, I guess, rather than an activist.
Anyway, she appears on a podcast talking about the urgency of switching to veganism. It features clips of Gary Yourofsky too (now, he IS an activist! And then some.)
The link is here. It's pretty gripping stuff, and the kind of thing I now tell people when they ask why I quit eating meat.