To the OP, I'm responding without reading any of the responses, so apologies for potential duplication.
1. I don't like kids as a general concept.
2. To do it right, it seems it would have to become the most important thing in your world. I'm not interested in making it so but I would worry constantly that I was doing a mediocre job.
3. I couldn't care less whether my genes make it to the next round.
4. I observed how having them affected my sisters' outside interests and the quality of their marriages and didn't want to risk the same happening with me. Seeing the same thing happen to friends who had kids reinforced this.
5. I'm the youngest of six and saw how much more my parents seemed to enjoy their lives when most of us had moved out.
6. Average cost of raising an American child to age 18 is something like $185,000. Given the above, unfavorable cost/benefit ratio.
7. The woman I wanted to marry had all my reasons plus no interest in being pregnant.