Long-term should be defined. We can cool the planet the same amount long-term. Why is it taken as a given that any warming is irreversible when we have historical natural patterns showing global cooling (ice age)?
Of course it can be reversed, it’s just vastly more expensive to do so. If your house is on fire and you don’t have insurance you don’t say “eh I can just build a new one”, you put the fire out.
I agree that warming is an important issue to address. I don’t agree that we know that it will be more expensive to cool. Space is cold and technology allowing heat to vent into space may be less expensive than we think.