The admittedly rather silly way I've framed this in my own mind is to ask if it was ok for, say, people living in Rome during the fall of the Roman Empire to have kids, living as they were through the total collapse of their civilization.
In retrospect it seems more silly (to me, anyway) to suggest that they shouldn't have had children because the children and their descendants would have had a hard time living through the collapse and ensuing "Dark Ages."
Their very distant descendants would have gone on to live through the most prosperous period in human history, which certainly wasn't foreseeable to the people living through the bad times.
Before anyone says that it's not comparable because the Roman Empire was just a small part of the world, and that we're destroying the whole world through climate change, I would suggest that for people living in Rome back then, Rome would have felt like the whole world and the vast majority of people were unlikely to uproot and move more than a few tens of miles, nevertheless, the population of Rome declined by, what, 99%?
In addition, most of the worst case scenarios for climate change seem to indicate the displacement of a few billion people at most, which would be terrible, to be sure. But the mere migration of a few billion people will probably be insignificant on the timescale of a thousand years.
More permanent destructive changes to the environment could cause massive human death, but I personally haven't seen predictions on the order of 99% of people dying (or anything remotely near that) and it seems like there's a pretty good chance that a new equilibrium would be reached at some point and the population of the Earth would surge again. Even the worst predictions seem like they could end up being inconsequential on long enough timescales.
And this doesn't even address the whole Idiocracy situation where arguably the best way to combat a dire future could be to raise kind, compassionate, conscientious children that will go on to steward the world onto a better path.
Needless to say at this point, I'm not convinced that it's remotely unethical to bring children into a difficult world. That's been the state of the world for basically all of human history.