This is one of those philosophical questions that have no "correct" answer but heres my take on it. Also sorry, this turned into an essay but I was on a roll

The main thing is that having a child isn't something the parents do for the child. You can't do anything for a child that doesn't exist. Having a child is something parents do for themselves; they want a child so they have a child. Plus an unborn child can't possibly consent to being born. Put those two things together and you have two people doing something that they want to do for their own benefit which fundamentally changes the state of being of another person who can't possibly consent to it.

When you have a child you are also taking a gamble on how their life will turn out without consulting them. They could wind up being the happiest person in the world who lives a full perfectly fulfilled life. Or they could wind up absolutely miserable for the rest of their life wishing that they have never been born. Both of those things are largely up to random chance.

For example my brother in law was born to a homeless single heroin addict and grew up on the street even after his mom died. He is now a professional engineer with a doting wife, a loving family, and a large house with a white picket fence in a fairly nice neighborhood. He now literally lives the steriotypical american dream except he has a cat instead of a dog. Sure he worked for all of that but even he will tell you that it also just required a lot of luck. Meanwhile my foster brother was born to a happy, healthy, loving, and even relatively wealthy family but due to a freak illness when he was barely a toddler he now has next to no motor function. He can only slightly move one eye and eyelid but even that is taxing for him. He can kind of control a tablet with eye tracking for brief periods of time before it exhausts him and he likes to wink at people to say "hi" but that is the extent of agency he has in the world. He will almost certainly be like that for the rest of his life.

When you have a child you are taking that chance without consulting them. Some people see the chance of their child living a good life as being worth the risk, which is a perfectly acceptable opinion to have. Don't take this as me saying people need to be ashamed of having children. Like I said, there is no correct answer here. Other people (myself included) see it as unethical to take that risk for someone who can't consent to it. I obviously lean that way due to personal experience. I also don't see much point in creating more children when there is even one child that doesn't have a happy home. My genes aren't anything special, why make a new child when I could even possibly help an existing child have a better life.