"You shall not
murder." (Ex. 20:13)
20:13. murder. Hebrew, like English, distinguishes between "murder" and "killing." "Murder" refers only to the taking of human life, and it is subject to the death penalty only when committed with malicious intent. The cases of manslaughter, killing through negligence, killing in war, execution for crimes, killing animals, animals killing humans, and human sacrifice are all treated separately from this in teh Torah, and terms other than "murder" are used. (On the special circumstance of the one who murders without malice, see Deut 4:41-42.) At the same time that I am writing this, technology has raised new cases, including abortion and assisted suicide. Whatever one's view of these matters, one cannot simply claim that they are prohibited by the commandment against murder. One must argue whether they are consistent with the other cases that constitute murder or if they belong among the cases that ivolved taking life but still are not murder.
-Richard Elliot Friedman Commentary on the Torah
Have you ever even READ the Torah? Those three-thousand were no longer his followers, but were now following a creation of their own hands, which was not YHWH, who had brought them out of Egypt. They had committed a capital offense of the time, and were executed.
Nowadays, it's against our laws to execute someone for their beliefs, and thank goodness. But it's inappropriate to judge a piece of literature from antiquity by our own standards. (Especially since our own standards are very low, apparently.)