It's absolutely why their stock crashed. Fb lowered their guidance for upcoming quarters mostly in expectation of slimmer gross margins. Since the top-line revenue isn't expected to change, the decrease in margins is by definition driven by increased costs. This increase is directly connected to Fb's efforts to (manually) police more content. Zuckerberg even explicitly warns of this occuring in one of last year's earnings calls.

I'm pretty sure that's what analysts are saying. The biggest cause was the drop in earnings and projected earnings due to increasing spend on security. It's not all the moderators but it's all part of the same push.

And on features that have lower potential for monetization, but higher user engagement like stories.

This is certainly part of why their stock crashed, they explicitly mentioned in guidance that this would hurt their profitability in a major way.