this is super frustrating, as platforms such as Facebook and Twitter claim to be the digital equivalent of the "public town square" yet take on none of the responsibilities and transparency that come along with it, just all the profits.

I would suspect something a bit more sinister: the very organizations you are targeting probably started a mass campaign to "report" your content, which triggered automated systems that caused your posts to disappear. A more cynical me would add in the fact that any manual review by Facebook staff would trigger even more aggressive moves to silence you, given that you're directly accusing them of inadequate moderation of their platform, which at best doesn't make them look good, and at worst, means they lose advertising $$ that those groups may be spending with Facebook to target those very victims.