So, in summary, abstaining from sex is an effective form of birth control on 2 levels.
Causality is difficult to determine. It might just be that men with low sperm counts find it difficult to conceive. I had no problem.
It might be that men who find it difficlt to conceive shoot blanks.
The best thing to do for couples trying to conceive is to wait until they are both "desirous" and then have sex. Nature knows best. Why push it?