U.S. District Judge Thomas Parker handed down his ruling Friday, arguing the law is too vague and overly broad ... also saying it encouraged discriminatory enforcement. Parker says the law violates Americans' First Amendment right to free speech/freedom of expression.

Parker did make a distinction about obscenity -- which proponents of the law thought would help keep it intact -- but the judge struck that down, explaining ... "There is no question that obscenity is not protected by the First Amendment. But there is a difference between material that is ‘obscene’ in the vernacular, and material that is ‘obscene’ under the law."

He adds, "Simply put, no majority of the Supreme Court has held that sexually explicit -- but not obscene -- speech receives less protection than political, artistic, or scientific speech."

In other words, it ain't illegal for adults to talk sex or dress in drag in front of kids ... which is exactly what this law was all about in the first place. As you'll recall, this law banned public drag/cabaret performances where children could see them, and that might've created problems with the Pride demonstrations going on throughout the state this weekend.

It's interesting ... the judge -- who's Trump-appointed, BTW -- brought up a hypothetical example of a woman dressing as/impersonating Elvis ... and said a situation like that could be prosecuted under this law. While Parker did say the State had an express and righteous interest to protect its minors, he said putting a law like this on the books isn't the way.

As you know ... local Pride organizers there in Tennessee have reported receiving threats from various hate groups in recent weeks as they were planning their parades and events.