An organized disinformation campaign is what I would consider to be irrational argument and deserving of regulation; we already accept limits on deceptive and harmful expression by way of regulation and criminal legislation. Ie, one can't simply sell strychnine and claim it's a panacea, or defraud investors with cooked financials.

But that's different from a zeitgeist of individuals who believe in falsehoods and argue for what they believe to be true; any single one of which may be acting rationally and arguing in good faith.