I strongly suspect those calling for keeping killers around because “it’s a worse punishment” don’t actually want to keep them around - they want the killers to be killed multiple times, brutally deprived of multiple lifespans, in order to desperately somehow try to make up for what was taken.

They want to win a status game against the killers.

To do that, however, one would have to take other, dramatic measures, such as erasing serial killers to destroy fame, or harvesting them for blood or organs to flip their number into a net gain.  Both measures are dangerous.

The argument is also a justification to themselves because they know they’re supposed to be “civilized”.