“Artiste: First, men do not “have to have children”, it is a positive commandment that if fulfilled results in gaining a mitzvah. Not having children is not a transgression of this. Its merely non commission”
I thought that the mitzvah to have children, being incumbent on the men, comes with the LO SAASEH of not using any male form of birth control (as opposed to women, who can get a heter for certain forms of birth control under certain circumstances). It therefore stands to reason that men DO have to have children. They might not get an aveira for being unable to, but they surely are not permitted to prevent themselves from doing so.