You know the airlines’ rule about not taking liquids on board planes? The one that limits you to a few 3-ounce bottles carried in one zip-top plastic bag? The one that stops you from taking full-size sunscreen or bug spray or a nice bottle of California olive oil or wine onto a plane in your carry-on bag, so you can be sure it won’t break?

Well, what if I told you this rule was unnecessary and, in fact, could have been eliminated years ago? Would it surprise you to learn airlines may have an ulterior motive in stopping you from bringing larger-sized liquids onto their planes?

I usually don’t do much hardcore reporting in this column, but I have first-hand information from a former Federal Aviation Administration (FAA) senior official that the “liquids ban,” as I’m calling it, would already have been abolished, were it not for objections by the Association of Professional Flight Attendants.

Why do flight attendants like the ban? I could understand if it were for safety reasons. Goodness knows I wouldn’t want to go to work every day inside a machine meant for flying transportation, which terrorists could turn into a flying bomb. I sympathize all day long with the need for safety.

What I learned from my ex-FAA source was that flight attendants like the liquids ban because it gives them control over passengers’ behavior. Before the ban, some passengers apparently brought their own alcoholic beverages on board and consumed excessively, turning them into obnoxious morons. Flight attendants, as you can imagine, don’t like dealing with obnoxious morons. I can understand their position on the point, too.

What I don’t understand is why the majority of passengers need to be misled and inconvenienced, just to control the bad behavior of a small minority. And I’m more troubled by the word “misled” in that sentence than by “inconvenienced.” I don’t mind being inconvenienced if it’s for the sake of air-travel safety. I do mind being inconvenienced if it’s because airlines lack the nerve to take action to stop illicit drinking on their planes.

Laws stipulate that anyone opening a private space for public use has the right to control what takes place inside that space and — believe it or not — an airplane is a private space opened by airlines for public use. Airlines have, therefore, the right to control what goes on inside their planes. They could prevent passengers from bringing cocktails onto planes or from opening bottles after takeoff. They could confiscate open containers of alcohol. They could take any number of actions other than fibbing to the majority of passengers who behave decently, and they could allow us to bring our full-size liquids onto planes again.

What my ex-FAA contact told me when I quizzed him about the liquids ban, which had long struck me as an alcohol ban in disguise, was this: “The TSA is acting as a shill for the Flight Attendants’ Union.” If he’s correct — and he was in a position to know — then we, the flying public, need to demand the Transportation Security Administration and the flight attendants come clean and reconsider their policies. Passengers should be willing to do anything necessary to make flying safe, but we should not stand for being misled.

Let’s review some history. In 2006 the British Security Service (MI-5), with FBI help, arrested a group of British-based terrorists who allegedly were devising a liquid bomb, possibly using plastic soft-drink bottles. Shortly after the bust, media reported MI-5 felt it had been pushed into disrupting the operation prematurely, because the would-be terrorists had not yet made a bomb. They were basically still in the thinking stage and MI-5 wanted to wait until some actual work had been done, to have better evidence against the group. Ever since 2006, however, airline passengers have been prohibited from bringing liquids larger than 3-ounce bottles through security checkpoints. The head of Ryanair once spoke out against this restriction, but he was virtually the only airline official to do so.

During subsequent years, I’ve seen various clues suggesting the liquids ban concerned mostly alcohol. What struck me first was when no one ever checked the contents of those 3-ounce bottles. A few 3-ounce bottles of “shampoo” actually filled with gasoline could cause quite a bit of terror, I’d think, so I wondered if there was actually a terrorist threat.

Other clues included airlines discontinuing their routine announcement stating passengers were “prohibited from consuming alcohol not served by flight attendants.” TSA officers confiscated alcohol miniatures from passengers who were carrying them in their zip-top plastic bags. Gate agents have asked passengers carrying soft-drinks bought at airport vendors to pour samples of their drinks through filter-paper before boarding. (I don’t know of many liquids that are both potable and explosive — do you?) And notices printed on the sealed shopping bags used for duty-free purchases warn you not to open them until you get home, lest your purchases be confiscated. The statement by my ex-FAA source was, of course, the kicker.

One alternative to the current situation would be for security agents simply to use “swipe pads” on all full-sized liquids, to ensure they bear no explosive residue. If you pack full-sized liquids in your checked luggage, by the way, airport security usually opens your bags and “swipes” your bottles; I’ve seen it done. Additional measures could be to fine passengers who become obnoxiously drunk — or ban them from flying on the offended airline for a set time period. I’m no lawyer, but I believe such steps would be within airlines’ rights.

I’ve never personally seen an obnoxiously drunk passenger, interestingly, in my million miles of flying — and people who tell me they’ve seen them say they’ve been Business Class passengers who were being served free booze by flight attendants. My clues suggest the well-behaved majority are being punished for the sins of the minority, and it’s time to reconsider.