We like to think of the First Amendment as a shield for courageous but controversial speech.

But, like it or not, it can also be a get-out-of-jail-free card for jerks.

Case in point: David Earl Armstrong, 45, the Newport News man arrested and charged with obstruction of justice when he stood on a balcony on Jefferson Avenue and called out to guys about to get caught up in an undercover police sting:

“Those are the police! Those are the police!”

Technically, Armstrong wasn’t wrong.

The “prostitute” on the street luring would-be johns was an undercover policewoman. Other cops were ready and waiting to make the ensuing arrests.

They snared 17 men that day, March 18, for prostitution-related offenses. They swept up Armstrong for good measure.

Now the ACLU says they shouldn’t have.

“An individual has a right to stand on his porch or on a public sidewalk and state what he sees about a police action,” Kent Willis, head of the ACLU of Virginia, said in the Daily Press. “We are a free society with free speech rights. This is a citizen merely announcing to other individuals what he observed.”

As miffed as I’d be as a police officer to have my undercover sting announced to the public by some guy on a balcony, I guess I see Willis’ point.

In fact, had the would-be johns taken a moment to make the same astute observations as Armstrong, they likely would have come to the same conclusion and skedaddled on their own.

It’s a little like drivers who flash their lights at other drivers, presumably to warn them of a road hazard up ahead or a (cough, cough) traffic cop.

Should they, too, be arrested for tipping off motorists about fishing holes just around the bend? For obstructing (cough, cough) ticket quotas?

Like they say, the First Amendment doesn’t merely protect speech we agree with.

It can also protect speech that screws up an undercover cop’s best laid plans.