Attorney General Eric Holder speaks about the 2013 initiative called "Smart on Crime," which directed prosecutors to limit their use of mandatory minimum punishments, Tuesday, Feb. 17, 2015, at the National Press Club in Washington. (AP Photo/Manuel Balce Ceneta)

On Friday, Attorney General Eric Holder issued a memo to everyone in the Department of Justice reminding them that they should not become customers in the commercial sex trade -- and not just because of the threat of extortion or blackmail, either.

"Regardless of whether prostitution is legal or tolerated in a particular jurisdiction," Holder wrote, "soliciting prostitutes creates a greater demand for human trafficking victims and a consequent increase in the number of minor and adult persons trafficked into commercial sex slavery."

While there's some debate, a 2012 study largely reinforces Holder's point. "On average," its authors write, "countries with legalized prostitution experience a larger degree of reported human trafficking inflows." And they have a scatterplot to demonstrate it.

It seems almost certain that the memo follows from revelations last month that agents with the DEA -- a branch of the Department of Justice -- attended sex parties hosted by Colombian cartels. We will note, however, that the general response to that news was not, "Oh, but prostitution is legal in Colombia." It was: "Pardon?"

Clearly, FBI agents and other members of the federal law enforcement system should not, of their own volition, be soliciting prostitutes where it is illegal. One hopes, fervently, that Holder's memo was not meant to remind his wards that they should not actively break the law; if that was its intent, the last few days (or, I suppose, weeks or months) before he leaves his position will be spent crafting a series of hundreds of similar memos. "SUBJECT: Prohibition on murder." "SUBJECT: Prohibition on scalping sports tickets." "SUBJECT: Prohibition on espionage." Et cetera.

The case for why those agents should not maintain the company of prostitutes hired by those they are investigating is slightly less clear-cut, but not entirely so. While the things to which I have been invited but which I'd prefer not to attend skew more toward the mundane than "drug sex parties," I think most adults have figured out ways in which to politely decline invitations that it's wiser for them to avoid. Will this become the new "If you're a cop, you have to tell me," litmus test from law-breakers? If so, I have all of the confidence in the world that our professional law enforcement agents will be able to figure out how to walk that line. And there will be a lot of prostitutes on standby near criminal activity, just in case.

Then there's the but-it's-legal-here! argument. This is what legal experts call "opening a can of worms." Sure, there are things that are illegal in, say, Singapore that are commonplace in the United States. And there are things in, say, Colombia that are illegal here. Hell, there are things that are legal in Washington, D.C., that are illegal in Maryland (although federal agents should probably avoid the particular thing I am thinking of). Laws are complicated and not always brightly delineated even within a jurisdiction (think: prostitution in Nevada). I hope very much that federal law enforcement officials know clearly where certain things are and are not illegal; I hope too that they don't use that knowledge to roam around in the gray areas.

Anyway. No more prostitutes, FBI agents! What I would do if I were Holder is go around and hand out the memo to everyone individually. The people who are like, "Awww, man"? Maybe investigate them, if you have the resources.