In 2016, President Barack Obama lifted the ban on openly transgendered people entering military service. His administration announced, further, that the Pentagon would pay for medical gender transitions. This was viewed as necessary lest transgendered servicemembers turned instead to suicide, or drug and alcohol abuse.

President Trump reversed this decision last week. He made the announcement, as is his self-destructive wont, via Twitter, making it essentally impossible for him and his administation to explain their rationale. A limit of 140 characters, or a multiple of that in a series of tweets, is not remotely sufficient to lay out a case for a complex and contentious policy. But Trump does not seem to care for making the case — his very similar snap announcement and lack of coordination on his "travel ban" was very similar — preferring to drop bombshells, letting critics freak out, and leaving it to his underlings to clean up the mess as best they can.

But, on the substance of the transgender decision (as with the travel ban), Trump, or rather Secretary of Defense Jim Mattis, is right.

To understand this decision it's best not to start with Trump, but to go back to Obama's earlier choice, made at the tail end of his term in office. Because of the nature of the military, the burden of proof for such a big change to its culture rests on the person proposing the change.

The military is unlike any civilian institution. Members of the military give up their freedom when they sign up to serve. Every enlisted person and officer is under an obligation to follow all lawful orders under pain of court martial, imprisonment, and possibly even death. This feature makes the military a tempting target for those who want to conduct fringe social experiments. Because military personnel must obey, they are in no position to refuse their commander in chief's orders, whether those orders are good or, as in Obama's case, disruptive, unnecessary, and bad.

The second unique feature of the military is that it is a purely functional body. It does not exist for personal enrichment, leisure, community, the pursuit of happiness, or for its own sake, as civilian institutions do. The military's sole purpose is to smash and destroy enemies. Even when it is merely used as a deterrent, the military's usefulness derives entirely from its ability to accomplish that goal in battle. This means all decisions about how the military is run should be subordinated to questions of military effectiveness, including morale, discipline, equipment, logistics, troop readiness and the like.

Our military regulations reflect this, exempting the services from rules that other employers must live by. There are many examples, but the relevant one is that the services not only reserve the right but actually have a mission-based obligation to discriminate in some cases where civilian employers would be sued for doing so. People with physical disabilities and bad health are routinely turned away. If you are over the age of 35, it's already too late to join the Army, Navy, or Coast Guard, and far too late to think about a career in the Marine Corps. The Air Force won't take you after age 39, and federal law forbids enlistment beyond age 42. Don't even think about bringing an age-discrimination lawsuit. You may think it unfair, but fairness isn't the goal.

Rules on military recruitment are based entirely on its goal of breaking things, killing people, and defeating enemies as effectively as possible within the laws of warfare. When Obama made his decision on transgender service and recruitment, it was not taken with this singular goal in mind. (He had a singular goal, which was to embarass his successor, just as President Clinton sought to embarass President Bush with last minute environmental regulations). This means the Obama transgender rule is not sacrosanct, much though the left-wing reaction to Trump's decision has been what it would have been had he been overtuning a time-honored and popularly supported tradition. It needs to be remembered that that's what Obama was doing, not what Trump is doing in reversing it.

Imposing a fringe ideology about gender differences that is not widely accepted in civilian life on hundreds of thousands of people sworn to obey creates logistical and morale problems, too.

By the time Obama permitted open service by gay men and lesbians in 2011, the majority of society had made its peace with that idea. This is one reason it has not apparently had severe consequences for morale or military effectiveness. Civilian society has not drawn a similar conclusion with respect to the idea that we can wish away the biological reality of sex and identify people as "he" or "she" when in truth they are she and he.

Can a person with male anatomy be a woman? Leftists opinion insists that the answer is yes. Yet people who are physically of one sex but think they are actually members of the opposite sex are regarded by most people and widely by the medical profession as having a psychological problem, not a physical one. In the argot of psychiatry it is called gender dysphoria.

The most generous thing one can say in argument with those who insist that men can be women, and women can be men, is that the question isn't even close to being settled.

Most people want to be kind and charitable, but it doesn't mean they embrace the idea that male and female are mere social constructs and not scientific reality. If they did, then most people attracted to men or to women (whatever their sexual orientation) would not insist on a partner who is physically and not just notionally male or female. Transgender activists point to this unavoidable reality as evidence of discrimination, but it is, rather, evidence that almost no one accepts the idea that a gender continuum can replace the biological concept of sex. If pressed in private on their discriminatory dating habits, the 99-plus percent of the population that harbor them would probably say it's because you can only stretch things so far, even in an effort to be inclusive.

That's the most glaring evidence that this issue is far from settled in civilian life. There is plenty of other evidence, though. The spectacle of biologically male athletes dominating women's sporting events is an obvious and natural source of controversy, not unity. The removal of legal protections against biological males openly inhabiting spaces reserved for women remains a serious point of contention as well.

Society might someday change its mind, setting biology aside to give inclusion precedence over fact. It has of course changed its mind on other, bigger questions more than once in recent times. If so, perhaps military policy on transgenderism will have to be revisited.

But the military services should be the last place where such such social changes are imposed, not the first. As Obama subordinated the military's mission to unrelated considerations, at the risk of complicating that mission, the reversal of his decision is the right course.

As tempting as it is to force controversial ideology on large groups of people who are obligated by law to obey, it is a cynical urge on the part of a radical commander in chief, and it should be resisted when military effectiveness is at stake.