Our Gemara on Amud Aleph relates a dispute between Rabbi Akiva and Rabbi Tarfon versus Rabban Shimon ben Gamliel. Rabbi Akiva and Rabbi Tarfon seem to understand the Torah practice of capital punishment as largely a threat and deterrent, but in a practical manner, avoided at all costs via legal mechanisms and various defenses to acquit:
Rabbi Tarfon and Rabbi Akiva say: If we had been members of the Sanhedrin, we would have conducted trials in a manner whereby no person would have ever been executed.
However, Rabban Shimon ben Gamliel objected as follows:
In adopting that approach, they too would increase the number of murderers among the Jewish people. The death penalty would lose its deterrent value.
The precise wording of Rabban Shimon ben Gamliel’s objection indicates certain nuances, particularly “they too” and “increase the number of murderers.”
The first clause, “they too,” implies another group. The meaning of this is likely: “Rabbi Akiva and Rabbi Tarfon are concerned about shedding blood and therefore seek to acquit the alleged murderers, but ultimately this will not save any lives because the lack of deterrence will embolden murderers and therefore cause more bloodshed.”
The second clause, “increase the number of murderers,” also requires study because in Jewish law, other offenses also incur the death penalty, such as desecrating the Sabbath. If Rabban Shimon ben Gamliel is concerned about lack of deterrence, why not also say, “this will increase the number of Sabbath violators”?
The simple answer comes from using our first textual analysis to answer the second question. Rabban Shimon ben Gamliel’s argument against Rabbi Akiva and Rabbi Tarfon’s leniency is more cogent if he proves that the reduction in bloodshed they sought to achieve by sparing the life of the offenders would be lost on the other end by increasing the number of murder victims. Rabban Shimon ben Gamliel could have also pointed out that this would increase other offenses as well, but that argument is less ironic.
Another answer is that even though Sabbath violation and murder are both capital offenses, murder is worse because of the social and emotional cost. Intuitively, we might feel that way, but religiously, should we not argue that God’s honor takes precedence? The simple answer to that is murder is not just an affront to society but no less an affront to God, so therefore it is more severe.
However, the Rambam has a different approach based on a Mishna (Sanhedrin 9:5), which discusses the case of a murderer who is obviously guilty but escapes conviction on some technicality. Such a person is killed anyhow via an indirect action of locking him up and feeding him in a manner that alternately starves him, then overfeeds him, until he dies of ruptured intestines.
This is quite a gruesome death, which seems even more severe than the official death he might have incurred. That matter itself requires study, but I suppose, in a way, the rabbis felt the manipulative quality of his dodging official conviction merited a more severe punishment. Perhaps even the nature of his death is ironic—alternately starving and engorging, hinting at a disordered and corrupt personality. Additionally, the death was still indirect, which the Rabbis might have felt was an overriding requirement since he was technically not found guilty, and thus they could not kill him outright.
Regardless, this punishment is reserved for murderers and not other offenses such as Sabbath violators. (True, the Mishna also inflicts this punishment upon a repeat offender of lesser prohibitions who receive lashes, but that is for a wanton repeat offender who has cast off any pretense of submission to authority. The murderer, however, apparently receives this punishment even for one murder.)
The Rambam comments (Laws of Murder and the Preservation of Life 4:9):
This measure is not taken with regard to other crimes punishable by execution by the court. If a defendant is liable for execution, he should be executed. If he is not liable for execution, he should be released. Although there are other sins that are more serious than murder, they do not present as serious a danger to society as murder does. Even idol worship—and needless to say, incest or the violation of the Sabbath—are not considered as severe as murder. For these sins involve man’s relationship with God, while murder also involves man’s relationship with his fellow man.
This Rambam highlights a point that we have commented on in other places, such as blogpost Psychology of the Daf Sanhedrin 84: The earthly Jewish court’s primary focus is societal preservation, not perfect or individual justice. Keeping God’s laws helps preserve society, but the Sanhedrin does not seek to exact precise consequences over every violation. The focus is most often on public and egregious violations that undermine the fabric of society. It is not that certain punishments are less severe, but the violations the Sanhedrin seeks to enforce are those that most threaten the functioning of society, not the actual severity of it in regards to the Heavenly Court.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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Rabbi Simcha Feuerman, Rabbi Simcha Feuerman, LCSW-R, DHL is a psychotherapist who works with high conflict couples and families. He can be reached via email at simchafeuerman@gmail.com