Is it more horrendous than what will happen if we just keep reproducing and using up the earth's resources?

I am not a humanist. World population has doubled in my lifetime, and when you weigh the tremendous pain and destruction that has caused and will cause, 3 billion extra lives that will witness (or their very close descendants) an unprecedented mass extinction/collapse event due their own sheer weight, I'm not sure that rampant uncontrolled population growth is not the thing that is morally horrendous. Just look what humans have done to this planet in 30 years. Insect populations down 75%, mammals down 60%, the Great Barrier reef is half dead, extinction rates are 1000x normal, habitat loss, trash in the oceans, global warming, climate change, microplastics, mass pesticide use, fuck....it's hard not to view humanity (at least in relation to literally all other life on Earth) through a very, very dark lens.

Yeah, given all this I don't think it's morally horrendous that most people would not be allowed to have kids. They can do literally anything they want with the rest of their lives, but FFS don't have kids.

So you see humans through this dark lens, but advocate for these same humans to decide who gets sterilized, then carry it out forcefully?

I don't see how this happens at all. Dystopian military force? And if someone tried, it'd be a major conflict.