dasiy,
don't feel guilty for having children, just because the canvas isn't perfect, doesn't mean you can't help to paint a wonderful picture. i have twin girls, and see some traits of mental illness in them, but try to give them coping tools that i have learned along the way.
as sweet put much better than i, it is environment that also effects biology. i have seen kids grow up with two addict parents and grow up to go to college and be very successful. then i have see the opposite.

children are the greatest gift in the universe. please don't regret having one. you can help paint the picture. none of us are perfect, all we can do is give it our all. day at a time, do your best, and please don't have regrets. just pass on what you have learned.
don't give up on yourself as a parent. we as parents help paint that picture, keep the colors bright and lively.
take care
grace