I don't see humanity building defenses against what likely caused those mass extinctions...

Agreed, humanity is unlikely to survive an asteroid of the likes that wiped out the dinosaurs, considering it increased global atmospheric temperatures to several hundred degrees celsius for a few minutes (or several thousand for a few seconds) (https://www.youtube.com/watch?v=dFCbJmgeHmA).

It doesn't look like we need the help of celestial bodies intersecting ours, though. We're ushering in our own demise just fine on our own, thank you very much!

When and where are we currently ushering in our demise? None of climate models have us on trajectories close to global extinction - we are roughly on a 2-3 degree warming path at present.

This kind of doomsterism is just not useful.

I don't think you understand what that number means at all.

24K years ago New York was under 4 miles of ice, during summer. If that happened today, do you think the government of Canada and United States would survive such a schenario?How many people would be left alive in North America, 30% of the current population?

How big do you think the change in global temperature was during the last ice age? 30 degrees or 20 degrees?

It was only 6 degrees. That's all it takes.

Average yearly temperature for Hong Kong is 23 degrees, for Dubai it's 26 degrees.

3 degrees is the difference between lush tripics and a desert where you will starve because nothing grows.

A global change of 3 degrees means 12 degree change on land because 70% of the planet is an ocean and it's tempersture doesn't change

Who is seriously claiming catastrophic collapse on the 2-3 degrees increase trajectories?

Literally anyone who studied impact of changing climate on food security. And we will not see a warming of 2 degrees, we are on track for 4 - 6 degrees. The 3 degrees scenario is only projects due to fictitious 'negative emissions' from carbon capture, which will cost many times more than the current revenues of the oil industry. It's pure fantasy.