Your other examples don't match the "sufficiently harmful" criterion, besides being unresearched nubjects at the time of debate. But eg white supermacism does - it's also a contrarian theory - and it's rightly banned.

Re: eventually - in climate change it's a case of long run vs short run, as Keynes put it: "The long run is a misleading guide to current affairs. In the long run we are all dead. Economists set themselves too easy, too useless a task if in tempestuous seasons they can only tell us that when the storm is past the ocean is flat again."