You think that you can "deal harshly with such hatred/disinfo campaigns, ruthlessly deplatforming fringe elements and denying them the chance to drag the Overton window their way" forever, because if the right people run it, they can keep the wrong people from ever coming to power. That's misguided, for two reasons.

First, sometimes the wrong people come to power anyway. If they can't do it by blatant misinformation and propaganda, they'll do it by "wolf in sheep's clothing" tactics. Once they get power, the machinery is there, just waiting for them to use it to enforce their narrative. Sure, by protecting the narratives that are allowed, you might make it more difficult for such a one to come to power, and therefore less probable. You can't make it impossible, though. And if the thought of such machinery in Orban's hands (or Trump's) doesn't terrify you, you're not thinking.

Second, power changes people. You might be a perfectly fine, democracy-loving person. Give you that kind of power and you might not be the same person forever. As Elrond said, "I fear to take the ring to guard it. I will not take the ring to wield it" - and for very good reason. Too much power is a danger even to the good.