Putting aside whether having children is a topic that should be brought up before tying the knot, grieving over how their child may resemble the negative sides of themselves, especially during that vulnerable time, I think is a valid concern to have.
With my 'mental health problems', despite arguments whether such problems are genetic, I'm worried how there's a chance my kids would inherit those and turn out worse in today's times than I have. I wouldn't want anyone to experience the same struggles that made it difficult for them to fit in and understand people as I have (still have issues with those to this day).