Discussion and user participation. If you're an admin of a non-political reddit and want to further a political cause ("reddit meta" is political in my book. this point is debatable.) open threads, let people know. If people are interested, the post counts and ratings will reflect this. If not, it'll die off.
Want to do a blackout? That's somewhat extreme, but also fine! But how about announcing in advance? How about polling your users? Maybe the vocal minority are giving the wrong impression and a good 70% of your sub's users couldn't give two shits. What happens then? Should the fact that you're the community leader in a mostly a-political sub give you the right to say "fuck the users" and blackout anyway? No, it really doesn't.
inb4 the moderator's thread will be deleted because they're critcizing site policy. maybe. but not if so many major subreddits join together as they did now (the colluding itself is not wrong, again - the "holding people hostage" part is)