Cats survived before us by hunting small mammals and small birds, and they are very effective at getting fed.
The motivation at the core of naming owners of outdoor cats as irresponsible is a sharp decline in songbird populations in direct proportion to the increase in outdoor cat population.
Black-body radiation is an interesting argument against 100% efficiency, but couldn’t you just extrapolate and argue that the emission will be converted back to heat once it stops reflecting and becomes absorbed?