My impression is that celibacy pledges do something, although maybe not abstinence education, but I don't trust much of what I read, since it's so politicized. The article you link to says that it doesn't prevent sex before marriage, but that's a pretty high bar. The paper I was talking about (I added a citation above) says that it delays sex by 18 months; that just doesn't get you past marriage. Here is a paper that claims pledges do nothing, that earlier results didn't control for enough.

Let's not worry about absolute effect and instead look for robust results. I think it's robust that seeking abstinence leads to less birth control and a higher ratio of STDs to pregnancies. Also, the point of my original claim, about embattled minorities, is robust to that kind of selection bias.