It depends what you meant. The law doesn't give carte blanche to say whatever you want, however you want, either. Your example above is what libel and slander laws are about. People make (probably millions) of false claims about companies daily and none of them rise to the level of a credible accusation largely because they're done anonymously. Someone who could actually "convince millions of people" probably has at least SOMETHING damning, and if they don't, the backpressure from everyone else is going to be pretty intense. That's actually _normal_. Desirable.
_Some_ speech _does_ require freedom from damage because otherwise the direct effect is the chilling effect. Political speech is specifically one type of such speech. The internet really has forced us to look carefully at what kinds of speech warrant that protection and which don't and we clearly haven't figured it out yet.
But certainly giving that power to private companies - and removing it from the hands of the people, the government, the law, the courts, and posterity -- is _definitively not_ the right way to do it.
I think the really difficult part about all of it is, the areas that don't require protections, aren't because the speech isn't damaging, it's that an uneven application of the rules can lead to worse problems. Or issues where it's impossible to find objective neutral parties (a jury) to decide on issues central to politics.
If I convince millions of people that Example companies widgets kills kittens, when I have no reason to believe that to be the case, I would be held liable for the damage to the brand.
But the pseudo-anonymous nature of the internet and most platforms, and even trying to avoid problems like the Streisand effect allow damaging speech to avoid consequence.
I'm not advocating for any approach to fix the problem, this is just a curiosity of mine as of late.