> Harsh punishments work exceedingly well as a deterrent.
That is an enormous claim and there are reams of research on this topic - your assertion is not supported. It doesn't even stand up to the most cursory scrutiny - if it were true, then societies and states with harsh punishment would have lower crime - and this is very, very, very obviously not the case.
https://www.nij.gov/five-things/pages/deterrence.aspx
https://www.psychologytoday.com/blog/ethics-in-question/2015...
http://www.sentencingproject.org/wp-content/uploads/2016/01/...
https://undark.org/article/deterrence-punishments-dont-reduc...
tl;dr Social norms, accepted membership in 'legal' society and education are the best ways to deter crime, followed by certainty of punishment - not its severity. The reason people commit crimes is, in rough order, usually out of desperation, social norms that lead them to believe the prohibited act should be acceptable or ignorance of the knowledge that the prohibited act is illegal, for greed, and, lastly, then for the sheer thrill of it. Severity of punishment doesn't act as a good deterrent for any of those categories - certainty of punishment acts as a deterrent for the latter two, but for the first two, desperation and ignorance, are fairly well inoculated against rational counsel.
Before you start arguing the philosophy regarding merits of punishment v. deterrence, I am going to put it bluntly: the claim at issue - that severity of punishment is a deterrent for crime - is an evidentiary claim and it cannot be proven from first principle. It must be supported evidence, and as far as I can tell, the numbers are in, and they do not appear to be on your side. Unless you have studies that support your conclusion, the philosophy is totally irrelevant.