I'm in my mid-40's, and have yet to have any desire for children. My reasoning essentially has been that if I have children, they will either be like me, or not be like me. Neither of these outcomes encourages me.

If they are not like me --- well, I don't think there is any shortage of people in the world that are not like me. Further, I think that lowering the human population is the best thing we can do to prevent ecological collapse.

If they are like me, I fear that they too would be angry, depressed, ineffectual, and continually disappointed by the world. Reluctantly, I conclude that it's better for them (and probably the world) for them not to be, than to be like me.

(I'm sorry if this is an unhelpful answer. And while I'm unlikely to change my decision at this point, corrections to my logic would still be appreciated.)