Well, this issue is that these people are NOT abstaining and WILL not abstain, regardless of who tells them that's their best option. No one is arguing that it's not the best option.
But in reality it's NOT GONNA HAPPEN ... so it is imperative that you focus the NEXT BEST THING that will help prevent the spread of disease and pregnancy, which would be to wear a condom.
I really can't imagine that this is a hard concept to grasp. There's no way in the world you'll ever get people to quit having sex, regardless of the risk. The world and people aren't perfect, and to expect them to be as the only solution is about as ridiculous as anything I could ever imagine.