God created the world with a process that involves sexuality to bring more people to existence to serve him. It doesn’t seem sustainable; if everyone achieved the degree of spirituality that the continent clergy has, then the population would decrease and no more people would serve God. 

Why would God benefit from the prohibition of an act which gives existence to other humans that will potentially also serve Him?

I read the argument “better focus to serve God by ignoring sexual impulses and distractions,” but in that case having children while controlling sexual impulses and abstaining from time to time makes more sense.