I'm against the death penalty in general, but I also acknowledge that in terms of tangible damage to humanity, any billionaire walking the Earth makes any serial killer who has ever walked the Earth seem positively quaint by scale.
I also recognize that we are living under class occupation. The owner class handily won the class war by convincing most of the developed world not to fight it half a century ago.
The peasants don't have the luxury of taking prisoners. We are the losers of a war, in spite of the fact that many have come to worship their occupying oppressors.
Keeping the most destructive humans locked away and well fed until they die of natural causes is a peacetime luxury for those in charge, and unless you're holding a reprehensible amount of capital, that isn't us. You might believe we are in peacetime, but if we refuse to stop them, and it looks that way, they will force our shared, communal habitat to stop us all through their insatiable, sociopathic avarice.
We love to think we're not, but we're still subjects wholly dependant on this world, even the owners activily attacking us and it simultaneously.