Such an interesting question that's so hard to rationally answer. Honestly I have cursed my parents many times when feeling utterly depressed and anxious for having kids in the first place. Didn't they know they were going to pass on these traits?
In their defence, they have actually visited their GP with this exact question; what is the risk of genetic predisposition for depression if we are to have kids? The authority figure in the white coat (as I imagine he was wearing at the time) said 'no, don't worry, it's all in the upbringing'
And although I do share the idea of a nature / nurture combination for the perfect storm, I don't buy that it's a 50/50 equasion. Since your nature (genes) influence your behavior, your nurture will change, probably for the worst. Plus, the people raising you haven't really properly been nurtured either.
Still I'm torn on the question myself, when I feel fine (which ocasionally still happens), I'm actually quite positive about having kids, even though I have learned the hard way that it's probably best not to. Plus, this depressive gene or genetic combination seems to be very dominant in my family, not only do all my aunts and uncles (from my dads side) have low mood issues, almost all of their children (my cousins) do too.
Now, I'm just waiting it out, becoming too old to reasonably still start a family, while everyone around me is either actively reproducing or has reproduced multiple times over
Oh PS: and then they bitch and whine about 'you've got such a great life, you can still go on vacation anywhere' om some shit like that.