The benefit of a free exchange of ideas is that it allows people to originate and develop the ideas that we later recognize are correct in hindsight. The eventual move towards masks wasn't inevitable; there are some countries even today where masks aren't broadly recommended, so if Internet platforms had banned mask advocacy in March there probably would have been a lot more.

(I'm not sure this is on point to Youtube's policy here, though - they say they aren't banning all vaccine skepticism, just specific categories of silly disinformation like microchips.)