You wrote:
“Read the passage.”
Already have - many times. You’re about to prove my point for me.
“They secreted idols under their tunics and God killed them in judgment because of it.”
They wore amulets - pagan amulets.
“If it were merely superstition they would not have had to deceive.”
Sure they would. Such superstition is a violation of the first commandment.
Protestant commentators regularly get it right:
William Barclay, for instance, wrote:
“Prayers for the dead are a much-disputed problem which we do not intend to discuss here. But one thing we can say–to the Jews prayers for the dead were by no means unknown. In the days of the Maccabean wars there was a battle between the troops of Judas Maccabaeus and the army of Gorgias, the governor of Idumaea, which ended in a victory for Judas Maccabaeus. After the battle the Jews were gathering the bodies of those who had fallen in battle. On each one of them they found “things consecrated to the idols of the Jamnites, which is forbidden the Jews by the law.” What is meant is that the dead Jewish soldiers were wearing heathen amulets in a superstitious attempt to protect their lives.”
That's not what is written.
40 And they found under the coats of the slain some of the donaries of the idols of Jamnia, which the law forbiddeth the Jews:
41 Then they all blessed the just judgment of the Lord, who had discovered the things that were hidden.
42 And so betaking themselves to prayers, they besought him, that the sin which had been committed might be forgotten. But the most valiant Judas exhorted the people to keep themselves from sin, forasmuch as they saw before their eyes what had happened, because of the sins of those that were slain.
God killed them because of the sin of idolatry.