Word for people who just comment rather than act on something

Solution 1:

If they are reading and commenting about it after the fact, I’d call them “Monday-morning quarterbacks.”

If the event is still occurring and they don’t have the skills, means, and/or opportunity to do anything except comment or complain, I’d call them “Armchair quarterbacks/generals" or perhaps even “kibitzers.”

Finally, if it’s still occurring and they do have the skills, means, and opportunity to help but lack the enthusiasm or concern to extend their involvement in the issue beyond that of merely commenting on it, I’d call them “apathetic/complacent/indifferent (and/or if the consequences of their inaction so merit, even)/depraved-heart/heartless observers.”

Solution 2:

Slacktivist seems to fit (especially online), if their comments are intended to get people to agree that something is bad but they don't actually do anything about it or contain a "call to action" besides "Like this post".