> Right, but that is not how the law is applied. In a civil lawsuit, court or the government is not the plaintiff or the defendant, and therefore first amendment protections do not apply.
It absolutely is, which is why thr First Amendment limits the conditions in which civil defamation damages can be awarded, see, e.g., Times v. Sullivan.
EDIT: In fact, Times v. Sullivan rejects this specific argument, saying: “Although this is a civil lawsuit between private parties, the Alabama courts have applied a state rule of law which petitioners claim to impose invalid restrictions on their constitutional freedoms of speech and press. It matters not that that law has been applied in a civil action [...]. The test is not the form in which state power has been applied but, whatever the form, whether such power has in fact been exercised.”
> There are first amendment protections when public officials are involved in the defamation suit. But beyond that, it is well established that first amendment does not protect this kind of speech.
This is completely wrong. Times v. Sullivan, the landmark case applying the 1A to defamation, and subsequent cases elaborating the Constitutional limits of defamation liability established both basic 1A rules for all defamation cases, and additional rules for public figures (not just public officials, but also others who seek public attention), and matters of public concern. Among the rules applicable to all cases, not just public figures and public concern are:
(1) Opinion is Constitutionally protected and cannot be defamation (as it could be in some jurisdictions before),
(2) Falsity is required element of defamation and must be proved by the plaintiff, it cannot be presumed with the truth as a defense (as, again, it was in some jurisdictions)
(3) Fault (at least simple negligence) is a Constitutionally-required required element; defamation cannot be strict liability (as, again, it was in some jurisdictions prior to the Constitutional rule being articulated by the Court),