People don't want see other humans for the profoundly evil, or at the very least reckless, beings they are. I believe that this true for reasons of mental health.
A good example of this is ethical Veganism. And I use the word ethical to separate this type of Veganism from the one that is primarily associated with avoiding animal products for health reasons.
I remember reading online about a guy who said he stopped being vegan because he didn't want to see his fellow humans as unrelenting murderers (although he didn't use those exact words). Which is where you will end up if you follow the ideology of ethical Veganism to its logical endpoint. If it is wrong to cause harm to any sentient being for any reason and virtually all humans engage in this behavior on a daily basis primarily for reasons of pleasure and tradition, then that paints a very ugly picture of humans.
Dima is being painted as a stubborn, immature person because he is not leaving any room for a positive or neutral view of parents. And parents (as well as future parents) constitute the vast majority of human beings in this planet. We don't want to see the vast majority of the people we interact with as bad, irresponsible beings so we paint the person who calls them that with that same brush. Better that one individual than the rest of humanity.
This is also a way for us to feel like we are in control. We know that there isn't any way for us to stop any of the horrors that happen around us on a daily basis, so we begin to make everything a matter of personal choice. It's okay for people to have children if they want to. The fact that bringing children into this world inevitably puts them in harm's way is ignored and brushed aside even though that was what the argument was about initially. The closest we ever come to including morality in discussions around childbearing are statements like "as long as they can afford them." I find that statement (and attitude) woefully wanting in several ways but that's a post for another day.