The Home of Spock/McCoy Fiction
Spoilers for ST III: The Search for Spock and ST IV: the Voyage Home.
Things get understandably awkward after Spock knocks up David on Genesis, but that doesn't explain why McCoy is so mad. David just wishes this miracle of life business doesn't interfer with getting together with Saavik.
McCoy makes a deal with an advanced race of aliens visiting on the Enterprise, one that doesn't quite work out the way he expected. Nor the quite way aliens meant it to either.
Spock does not have a need for the belief personally, but he understands the human desire.
(It takes McCoy years to get him to have a drink.)