Says who? This kind of attitude is what fuels extremism, as it represents a breakdown of negotiation, dialogue, and consensus-building. Every enduring society has rules about what is acceptable. Rules in themselves aren't inherently tyrranical, if they contribute to the common good.
Parents have every right to object to material in schools they deem indecent. It's real tyrrany to suggest that they should just shut up and trust so-called experts, who do not necessarily have their interests at heart, and who don't have to be around to pick up the broken pieces of broken lives left behind, in their libertarian fantasyland conceptualization of ethics.
It's the denial of the right of society as a whole to have any kind of norm that is the deeper problem.
You say that likes its some kind of historical inevitability, like a society can't destroy itself through internal conflict (it's happened before, like in Weimar Germany, until the bulk of Germans, tired of fighting in the streets and the filth in theaters, sided with the fascists). If that doesn't disturb you as a real possibility, you simply aren't being realistic, or worse, you don't care.
