This has some teleological problems. When you make an important breakthrough, there are innumerable factors which contributed to the breakthrough happening. It feels tempting to say "if I hadn't been born, this breakthrough wouldn't have happened". But to the extent that's true, it's also true that if you hadn't read a certain book, or had a certain teacher in the third grade, the breakthrough wouldn't have happened.
It's also often just false though: if you had never existed, someone else who read the book would have made the breakthrough - probably not too long after! (see steam-engine time) By this reasoning, writing books, being a teacher or any other number of things are better long term investments than physically creating a child.
> Of course they are some bad apples but that's mostly due environment factors
Breaking out some personal information now: I was raised in an abusive home. I was deprived of a traditional upbringing/education, and have spent most of my adult life learning how to be an adult.
I've also found success, but it's been complicated.
One thing I know for sure: having kids will never be the right thing for me, and that's ok.
Everyone has a different situation, but your commentary does not leave room for the wide spectrum of circumstances that people are dealing with.
> but your kids might do it or their children so you could say children are a good long term investment
Or they might not. To have kids solely for this reason is extremely questionable.
Arguing about kids vs. cats is not useful if you don't consider the many factors that should be considered when having kids, even if the focus of your argument is one of environmental impact. For example, say I choose to have kids purely because I thought that might someday save the environment, but ignore the fact that I'm not well equipped to raise children to begin with (a factor that lessens the chances of future success), my plan starts to sound like a pretty bad one.
An earlier comment pointed out that many younger people are deciding to have pets instead of kids. That comment did not explore why. Without understanding why (I added my why as an anecdote), any argument about the baseline merits of one vs. the other is not going to be an argument worth considering.
Of course there are some bad apples but that's mostly due environment factors.
I still believe that when you have to choose between a cat and a human being you should bet on the human to solve the eco problems.