There is a yawning abyss of states in between extinction and 'boy sure is a few degrees warmer out here' and none of them are good.
Many organisms would benefit from a warmer climate, just not humans.
We rely on extremely narrow conditions for the fragile supply chains and power structures that keep us on the ragged edge of civilized to continue working. We had an extremely mild contagious disease outbreak, by historic standards, and our economy is still feeling the effects!
Imagine the impacts of something like wildly different rainfall patterns, increased rate of global infectious disease, shifted agricultural zones, changes to Jetstream patterns, large scale crop failures, loss of water supplies, temporary local ecosystem collapses etc. These changes are incredibly fast on the scale of what it takes to reach ecological equilibrium.
These of course mean nothing to biological life, writ large. Life will recover and adapt. To fragile human civilization they mean refugee crisis, resource wars, failed infrastructure, and ten thousand other existentially terrible things.
