I'm not sure what you mean by Extinctionist. But I will say that many who understand the situation choose to go Vader and would rather go down the eugenics, pogroms and impoverishment of "others". Any good idea can be corrupted by assholes.

Overshoot has a price to be paid in lives through conflict and deprivation. I believe it is preferable for that price to be paid by people never having been born in the first place. It is a key pillar of Degrowth.

Edit: I'm fully aware of other variations and "solutions" to the predicaments we face. I'm just saying of all the possibilities and modalities, if you want to rank :minimize suffering" as a no. 1 goal. This is the way to go.