--Maybe they weren't idol worshippers at the time because Yitro was at first the Priest of Idol Worshippers, he then dropped everything and went against idolatry. Perhaps Moshe already saw that in Tzipporah his daughters (in fact I think that they were fighting against Yitro's daughters precisely because of this specific reason- because Yitro renounced idolatry).
--Or another reason- since the Torah wasn't given yet, maybe Moshe didn't know the Halacha.
http://www.torahaura.com/Bible/Learn_Torah_With/LTW_5761/LTW_5761_Yitro/LTW_5761_Yitro_Stalh/ltw_5761_yitro_stalh.html
After the Exodus from Egypt, Jethro brought Zipporah and their (the text says, “her”) sons to Moses, who had led the Israelites to the Sinai territory. Having heard that Hashem had rescued Israel from Egypt, Jethro blessed Hashem and declared Hashem to be greater than all the other gods. He then brought a sacrifice to Hashem and shared a meal with Aaron and the elders of Israel. Later Jethro gave Moses sound counsel about the administration of justice among the Israelites. It is to Jethro’s credit that the parashah containing the saga of the Revelation of Torah bears his name, Yitro.
Yet Jethro as a convert received mixed reviews among the Rabbis. A minority of those I consulted looked upon him favorably. Even before his initial encounter with Moses, they observed that Jethro had resigned as a priest. By then, he had concluded that idol worship was worthless and therefore abandoned it. In response to his renunciation of pagan worship, Jethro’s community excommunicated him and his daughters were forced to assume the traditionally male role of tending the sheep. (Exodus Rabbah 1:32)
When Moses sent Jethro away from Sinai before the Revelation, some Rabbis believed that Jethro had left to spread the knowledge of the true God among the Midianites. (Tanhuma B., Exodus 73)
It was in the interpretation of the phrase “Va-yihad Yitro—And Jethro rejoiced” (Exodus 18:9), however, that we can boldly see the Rabbis’ ambivalence toward Jethro. Some maintained that Jethro had genuinely accepted a belief in one God. Hence they understood the word Va-yihad as a derivative of the root YHD, meaning that he had declared God one. (Yalk. Sh. Yitro 268) Others, however, understood the word Va-yihad to be derived from the same root as hiddudin, meaning “goose flesh.” In other words, to these critics, Jethro had developed goose flesh because of his agony over the plight of the Egyptians. (b. Sanhedrin 94a)
Umm point one is not possible... He saved the daughters of Yitro before he even met Yitro... How could Yitro have renounced Idolatry before Moses arrived? Yitros conversion did not happen till after the splitting of the sea (when yitro came to visit the Am in the desert)...
Umm point one is not possible... He saved the daughters of Yitro before he even met Yitro... How could Yitro have renounced Idolatry before Moses arrived? Yitros conversion did not happen till after the splitting of the sea (when yitro came to visit the Am in the desert)...
So today, it's permissible to save the drowning idol worshiped for the life risk to all of us, but does the prohibition of saving the Jew who isn't shomer shabbos apply?