Malthusians versus pro-natalists: whoever wins, we all lose (our civil liberties)!
I'm going to have to write two arguments here, because you're both wrong. The Earth is nowhere near carrying capacity, every advanced economy is looking at underpopulation. At the same time, however, forcing people to breed is inhumane and counterproductive.
The root cause here is economic inequality. A large part of environmental damage is caused by a handful of outsize polluters who manage to escape prosecution and liability. People don't have kids because they don't have economic opportunity, because it's been eaten up by perpetually enshittifying monopolies. Who are also those same outsize polluters.
Examples of outsize polluters include things like the fishing industry, responsible for one of the largest streams of plastic pollution into the oceans. The agricultural industry uses a majority of the American midwest and west's water, deliberately wasting it in order to retain the legal right to use it in the future, "just in case". And 30% of US greenhouse gas emissions is just industrial emissions.
Examples of fertility rates being tied to inequality include countries like South Korea. For the record, almost a quarter of all of South Korea's economic output is just Samsung. 60% of their GDP is chaebols[0]. The chaebols control the political system to a ludicrous degree[2]. They have such deep ties that the South Korean CIA will literally have people writing down the names of people involved in protests so they can add them to Samsung's hiring blacklists. Who the hell would want to have children in such a country?
Malthusianism fails as a political philosophy because it ignores the distribution of resources and treats reproduction as a scarce resource that needs to be limited (specifically to ourselves, and people like us, or people we like, etc). This makes it apt for coopting by exactly the kinds of people consuming Earth's limited resources to shift blame.
Likewise, pro-natalism wants to blame the victims of income inequality for not having lots of children. This is specifically because it's easier than actually breaking the power systems that are fueling the inequality.
[0] Korean for zaibatsu[1]
[1] Japanese for chaebol[0]
[2] Every South Korean president since the country democratized ends their term in a corruption scandal, followed by their successor pardoning them as a way to pay it forward to future corrupt politicians.