So far my best bets have been talking about the Demographic Transition Model - i.e, as wealth goes up, birth rates decline, so uplift the poor and we'll be fine.
I also say that we have enough resources to go around if we stop allowing 1 man to use the resources of 100.
Theres also people with mad conspiracies that the government is trying to decrease birth rates by promoting LGBT stuff. To that I've said I also say that the current system of capitalism is all about growth and making money, and more people = more money. They don't want to thin us down.
What else can I say? It seems to be a very common belief.
The entire continent of Africa produces 3% of global carbon emissions. Carbon production is basically exponentially associated with wealth. Making the top 1000 wealthy individuals live at the carbon emission level of the next wealthiest 1% would reduce carbon emissions more than the entire continent of Africa.
If they really care about environmental destruction, they should support wealth redistribution.
I like to use the stat: richest 1% of humanity are causing 20% of greenhouse gas emissions, the richest 10% are causing 50%.
and woke geoengineering technocrats don't care that their "carbon capture" grift requires stealing their farmland to plant trees