There are plenty of people with PTSD who have families (particularly, kids). Our reproductive age begins really, really, really early and our reproductive drive is incredibly strong. I don't know why mental illness like PTSD would in any way impact our ability to procreate as a species or at an individual level. It might make life more difficult and life might be filled with more suffering, but we're able to procreate under all kinds of bizarrely sub-optimal conditions.
One wonders if you could imagine anything that might in any way impact an individual's ability to procreate and have surviving offspring, if you don't see how significantly heightened suicide risk, being volatile and potentially dangerous to be around and restricted in normal functioning might in any way impact an individual's success in having surviving offspring.
Any psychological or physiological damage which doesn't noticeably dent your reproductive fitness, isn't -- at least as far as evolution is concerned. But being a mental wreck along the lines that PTSD is often portrayed very clearly would negatively impact your reproductive success.