I know your fear. I put off having a kid for decades because I didn't want to perpetrate my genetics on anyone. I got two suicides, substance abuse and three involuntary commitments in amongst all the bipolar. My dilemma is that either (A) my parents were so impossibly shitty that they fucked up with easy kids or (B) I really was a total pain in the ass. Neither position makes me feel warm'n'fuzzy.
You know, though, that if your kids ran into trouble you'd move heaven and earth to help them. You'd far rather that they lead normal productive lives but if they can't, you'll be there for them.