The "mute replies" button would be great, indeed. It would solve one of the issues with dogpiling. But other two remain:
- it discourages the participation of new users - because those are seeing the dogpile in full force, and they know they'll be dogpiled once they say something the local hivemind disagrees with
- it adds unnecessary noise to discussions - because it's a bunch of people saying the same shit over and over
Neither thing is welcome when you think about community growth.
And I can also point you to situations where dogpiling happens regardless of any reasonable stake the mods would have on that discussion. If it happens with or without editorial moderation, then editorial moderation is not the cause.
If you have data to show already, do it now.