I think it has something to do, too, with the way you were brought up and your own relationship with your mother.
My own relationship with my mom is pretty fragmented, and I've eventually come to the conclusion that cutting her out of my life is the best thing to do for my own emotional health. Now that I'm 24 and in a serious relationship, although not ready for kids just yet, I find myself thinking a lot about our relationship, how we got into this mess, and how I would try to avoid going down the same road with my kids. I'm well aware that I won't be able to be the perfect mom, but I would like to try and avoid the mistakes that my own mother made.
Sometimes, honestly, looking back at those times, I'm not sure I would be a very good mother, and I don't think I would feel comfortable bringing children into this world unless I could be sure that I could provide unequivocal love and support for them, regardless of how they turned out. I don't want history to repeat itself.