I never understood that phrase. If you admit there is virtue to your opponents actions isn't that just certifying you are wrong regardless of the opponents intentions?
No, it's saying they're doing something mostly superficial and useless because they think it will make people see them as virtuous, where they wouldn't have done it if it wasn't a highly visible act, not that the actions are actually virtuous. So like someone volunteers for one day for some charitable cause, but spends the whole time taking selfies and not actually helping much.
That said I'm not sure what the logic is that quitting facebook counts as this
Alright but the highly superficial act is seen as virtuous. The act we oppose when we use this phrase. That act. It is virtuous. Therefor we in this hypothetical stand against virtue and goodness.
An act being seen as virtuous doesn't mean it actually is. Or it could be only a little virtuous, but outweighed by how smug and obnoxious someone is being about it.
"gives more credibility"? Think about what consensuses various cultures through history and currently have arrived at about what is the right thing to do and who is worthy of admiration. Someone who assumes conformity = virtue would end up being pro slavery in most of those, public opinion on morality is wrong most of the time about most things, and pursuing it isn't the right thing to do at all, let alone the same thing as actually trying to be virtuous.
I look at history and I see countless peoples of all ages helping each other get by while individual opinions of fucking despots and warlords fuck it up for the rest of us.
Those guys also have an outsized influence over what someone would have to do to be seen as virtuous. The guy being pelted with rotten vegetables and publicly executed for opposing them? Not seen as virtuous. The guy running a church that does some good things but in a way that reinforces their power? Seen as virtuous.
Even if people are overall good, that doesn't mean they can translate that into successfully coordinating to come to correct collective agreement about complicated problems and be immune to elaborate efforts to distort their beliefs in particular directions. If you think, here is what people are saying about what I should do, so that must be an accurate expression of their combined good intentions, well no, it isn't, because that isn't something that is easily achieved by default.
It generally means that we don't believe they'd be taking that action if there weren't a camera rolling or trending hashtag to follow. It's not criticizing the actual action, but the context around the action.
We're agreeing that the individual act is virtuous. You're not understanding that complaints of virtue signaling are not criticizing the individual act. They're criticizing the unspoken lack of other acts.