There is an often quoted rebuttal to this which goes "this isn't helpful"

...I would say to those people, neither is being optimistic (i.e. unrealistic)

This person is not the best writer I'll grant you that...and an OS in forth isn't exactly the best way to prepare either but that's irrelevant to the central argument that we are...on a not particularly long timeline, doomed if we continue a pattern of behaviour that we have done now for 300 years.

It isn't being pesimistic to say we are in trouble here, nor is it "unhelpful" to be that way. Positivity and individualism were the two stick that we used to beat the world into the state it is in and the first step to fixing any problem is acknowledging it.

So you don't think it's helpful to point out the gun pointed at your kids? Ok let's do helpful stuff then.

We need to stop buying phones every year that are synthetically slowed down, we need to invest in public transportation that runs on renewable energy and reduce the number of gas and deisel engines in use significantly. We need to find ways to recycle the precious metal we painstakingly extract from the ground and we need to reduce our reliance on travel in a world where we can talk to anyone at anytime with virtually no delay.

But none of those things happen until you can get people to understand the inconvenient truth that this is not going to last and that requires you to put aside your feelings on the matter.

Responding to the truth with "this is not helpful" is...not helpful