The crew announced that for "security issues" the coach passengers were not allowed to use the restroom in the front (business-1st class) section even if you were seated in the first few rows .

I realize that the elite passengers do not appreciate the riff-raff from the cattle car coming up and peeing on their "priviledged seat" but how can it be a "security issue?"

We fly often and always find this amusing.

It reduces the number of people near the cockpit door.
It makes it easier for the crew to protect the cockpit.

Mark

On our flights(4) a few days ago, their restroom was at the rear end of the 1st class seats right before coach. It was maybe 10 rows or so until the cockpit.

That said, I see your point. Thanks for the response.

The toilet was probably inoperable in some way.

cdnyul's comments are spot on.

Even if you are flying in First, the instructions given to First class passengers is not to line up outside the restroom door to keep the area outside the cockpit clear.

I fly at least once a week (in Europe), and never heard such an announcement. Or anything on not lining up outside the toilets regardless of their location on board.
So I assume it must be either statutory US regulation, which you should find mentioned somewhere in the FAA's regulations. Or some self-made airline "rule" for whatever purpose they think is relevant and goes beyond legal requirements.
Usually, the (flying) public still responds best to the safety argument regardless how dubious the requirement is.