Apparently sperm counts are falling. While I think this needs to be investigated to find out why it is happening, should we really be pleased if human fertility falls a bit? It's not as if, just at the moment, there is any threat to the reproductive success of the species. It seems to me that, given a global population of over seven billion, in general terms reduced fertility might not be a bad thing. Perhaps we have been too fertile up to now.
That said, on an individual level, it would be troubling.
Nothing is ever simple.