As long as they stick to flagging/marking posts while keeping them visible I don't see how that's different from how HN works. Are you opposed to that as well?
HN never pretends to be neutral, it is a community with a set of rules. For example we even expect them to filter out-of-topic posts, and we know very well the opinions of the moderators / founders and where their line in the sand is.
However FB pretends to be neutral. If it's only flagged and there is no impact on the ranking algorithm, of course there would be no issue. It would just be a way to know FB opinion. But, frankly, we know better than that, of course the ranking and the reach will be impacted. This is even the stated intent.
