This is a slippery slope I think (even letting aside the fact that frequently such a cost-benefit invariably comes down to 'hey, the cost borne is skewed more towards the poor, while the benefits are skewed more towards the rich / otherwise privileged'). If we then also don't tackle climate change as strongly as we otherwise might, or work less to improve living conditions all around the world (since we now have a magic pill), then the long-term net effect is still bad.
That we discount the geographically and temporally distant too much, and the local almost not at all is a) what helps us locally survive & b) what causes our long-term downfall.
That we discount the geographically and temporally distant too much, and the local almost not at all is a) what helps us locally survive & b) what causes our long-term downfall.