Wow, some very thoughtful discussion,
I had a child and never thought I would, but spouse and I decided to at a late age. I wouldn't have, but the spouse, who changed their mind, decided we should give it a try. And this is a shared decision.
What I want to say is I believe vehemently that it is fine not to have kids, and this doesn't even need to be argued.
But I will also tell you from personal experience that having kids can bring out the best in you. It can and often does. Why? Because children are a raging ball of love. It's amazing, and it's hard not to see it. So, bringing them up usually raises the parents to a new level of trying and consideration and selflessness. Yes, it's a challenge, and things can go wrong, but for God's sake, have some confidence in yourself and in the world and make a vote for affirming the good in yourself and the world. It just takes a little faith, and I don't mean that in the religious sense, though that might help, too. And it can change you to be a more responsible person, and often does.
Being a parent can be a wonderful experience. It can be among the very best in life. And there's no reason it couldn't be. So please don't think that you don't want to pass along your bad character or the world is too uncertain, etc. You make the leap because you believe you can navigate it together.
Again, I believe it's perfectly okay to decide this isn't a direction for you. But I want to say to not make that decision out of fear. Parenting may help you rise above all that and in so doing, elevate the world in which you reside.