“And by your indication, most of people alive today are murderers. “
Those are not my definitions. Those fall under the definition of retzicha.
The premise of the poster was that just because someone doesn’t keep Shabbos does not mean they will be a murderer, that the person will not be over other aveiros. I just pointed out the fallacy of that statement because they would very likely be over on halachic retzicha. Precisely because those who do not keep halacha do not consider it murder, while the source of all that is true and factual, the Torah, does consider it murder.