I understand your good point.Yes, but there would be legal fees to get to that point. Sometimes punishment in itself. Look how this ‘bombshell’ accusation of murder has spread to be discussed as credible on reputable websites like this one.
I have no idea what prevents 1A suppression type lawsuits. As you stated they would seem to be a useful tool ala: "I don't like your speech. Here is a defamation lawsuit. Yeah, I know that I will lose. But, I can afford to spend the money to file it- you cant afford the defense."
At the same such opinion based accusations are routine on this forum. Yet.... the Forum has evidently never been sued for defamation. Likewise, defamation based lawsuits appear to be very rare.
I am thinking that they are rare due to a mechanism of some sort. Maybe courts routinely dismiss obvious 1A protected lawsuits out of hand? Or, the plaintiffs in such harassing 1A lawsuits can be counter sued for legal fees and penalties?