I believe the OP's point was that those things (Agent orange, tobacco <> cancer, etc) which our society almost universally agree upon were once, themselves, targeted by dis/misinformation campaigns.
And that if we are to allow censorship, we are allowing the potential for disinformation campaigns.
IMO, the flaws in this argument are that it assumes a disinformation campaign is something the censor entity is controlling (specifically the US military, in the Agent Orange example). It also assumes disinformation is the only tactic available to a bad actor to manipulate the public.
To the spirit of the OP's point, though, I think we need to be wary of any corporation pledging to make the world a safer place by monitoring our communications.
Of course the situation is not binary; there are things that should be censored. I would like our law enforcement to use any tool at their disposal to stop human trafficking. Murder is not cool, AT&T should help LE look into those as well. Politician Y is trolling the internet with lies; we actually have a toolset for that and it's called journalism. Understanding that journalism/media is actually part of the problem here doesn't mean AT&T can do a better job.