Myth: The Pharisee Jews who rebelled against the Seleucids were completely knowledgeably and observant of Jewish law (as we recognize it today.)
Fact: There could have been widespread ignorance about matters we consider pretty basic today.
Consider at length 1 Maccabees 2:31-41:
31 And it was reported to the king’s officers, and to the troops in Jerusalem the city of David, that men who had rejected the king’s command had gone down to the hiding places in the wilderness.
32 Many pursued them, and overtook them; they encamped opposite them and prepared for battle against them on the sabbath day.
33 And they said to them, “Enough of this! Come out and do what the king commands, and you will live.”
34 But they said, “We will not come out, nor will we do what the king commands and so profane the sabbath day.”
35Then the enemy hastened to attack them.
36 But they did not answer them or hurl a stone at them or block up their hiding places,
37 for they said, “Let us all die in our innocence; heaven and earth testify for us that you are killing us unjustly.”
38 So they attacked them on the sabbath, and they died, with their wives and children and cattle, to the number of a thousand persons.
39 When Mattathias and his friends learned of it, they mourned for them deeply.
40 And each said to his neighbor: “If we all do as our brethren have done and refuse to fight with the Gentiles for our lives and for our ordinances, they will quickly destroy us from the earth.”
41 So they made this decision that day: “Let us fight against every man who comes to attack us on the sabbath day; let us not all die as our brethren died in their hiding places.”
Two things spring to mind.
The first is that all those Jews in the cave were unfamiliar with the basic rules that mandates fighting on Shabbos. The second is that it seems that Mattathias and his friends reacted in manner that would suggest that up until then there was not perfect clarity on the subject. We see this by the fact that they litigated the matter. They brought up a compelling reason as to why fighting should be permitted—“If we all do as our brethren have done and refuse to fight with the Gentiles for our lives and for our ordinances, they will quickly destroy us from the earth”—and they came to a firm judgment as it says ” So they made this decision that day…”. Obviously, this matter needn’t have been adjudicated; it is, it would seem, obvious that the law is that one could break the laws of Shabbos to wage war.
Indeed the Shulchan Aruch, in Ohr HaChaim 329:6,7 is unequivocal on this.