I think you’ve misunderstood what was meant by that.
A long time ago Google didn’t check if an element was visible prior to indexing it, which encouraged webmasters to insert all kinds of extra junk in their page in the name of SEO.
Today Google doesn’t penalise sites for hiding elements, there are lots of legitimate reasons to do so, they just downrank the content which is concealed.
Hiding the content with a
display:nonemight backfire on you. We are giving hidden content way less weight in ranking.
Gary ‘Methode’ Illyes - Google
So unless your moderators are mission-critical SEO, this is perfectly fine to do.
Hiding their ads on the other hand? They’ll come down on you pretty hard for that.