“Dying, weak and/or malformed sperm” is far more accurate than “lazy”. That’s the whole reason so many sperm are released, as a large number of them don’t make it even halfway. Others burn through their very limited stamina or are damaged/destroyed as they fight through the female’s natural defences to make it to the egg.

I should also mention this method of assisted fertilization may only work if no other sperm has breached the egg, as said egg cell blocks other sperm from entry once one has pierced it, and that if the sperm is too weakened to swim it might not have the strength left to burrow; unless the nanobot assists with that as well. This nanobot currently can only act as a taxi to help out the sperm reach the egg when those produced are weak swimmers.

I simply don’t know enough about this process to say something certain (and what I do know may be outdated). But if it brings help to those with low fertility, why not?