I've heard the "1) Low Cost" is false. [1]. Mainly because it takes time and effort to actually execute someone, to give plenty of time to find evidence exonerating them. That delay and proceedings end up being way more expensive than just letting them live.

Re 2): Again from [1], I've heard executions are actually quite expensive. Thus, it doesn't scale well.

Re 3): It doesn't make me feel safe if somebody can frame me and get me killed. It makes me feel safer knowing I have time to prove my innocence.

Re 4): I am very skeptical of this claim. Any solid evidence for this being true? Anecdotal evidence shows the opposite. Most criminals don't have good long-term thinking skills, so they won't recognize the tradeoff between 40 years in prison and death, and use that to not commit a crime.

[1] John Oliver on death penalty: https://www.youtube.com/watch?v=Kye2oX-b39E