We can understand the Montana Meth Project’s decision to take down signs depicting a young girl selling herself to buy drugs.

The project is in the business of producing shockingly effective ads, but it also must hang on to broad citizen support. That can mean walking a fine line.

It is an unpleasant irony that the ad campaign, in order to influence its target audience, has to engage in shock tactics. And, like anything else, shockers become less shocking with time. There’s a feeling you have to keep upping the ante.

There’s no doubt that the ad in question was powerful, as are most Meth Project ads. And that’s precisely why the campaign has been so successful. Since it began, methamphetamine use by teenagers has fallen 45 percent. Meth-related crime has decreased by 62.

The program started by Thomas Siebel was carefully (and expensively) designed to work. The tender sensibilities of young mothers were not a major part of the equation. “Just say no” wasn’t exactly doing the trick, so to speak.

In any event, we were glad to see that the Montana Family Coalition, the main opponent of the “15 bucks” billboard ad, says it continues to back the Meth Project. That’s good, because the campaign really has earned our continued support. After all, as we keep reminding ourselves, potential new meth customers keep coming out of Montana elementary schools every year.

And speaking of well earned: That young model in the ad, with her look of stoic disgust at how far she had fallen, ought to get some kind of Oscar for her performance.