The Bible teaches that the remnant of Israel will come to Christ and be saved. Why should that disturb me? It is a glorious thing.
(and you are not entirely correct on the 2/3 number, but you are trying :))
"Prior to Israel's conversion, Zechariah predicts that two-thirds ("two parts") of the Jewish people in the land will perish during the tribulation period. Only one third of the Jewish population will survive until Christ comes to establish His kingdom on earth." (dispensationalist Tm LaHaye, Prophecy Study Bible, p. 991)
"According to Zechariah´s prophecy, two thirds of the children of Israel in the land will perish, but the one third that are left will be refined and be awaiting the deliverance of God at the second coming of Christ which is described in the next chapter of Zechariah." (dispensationalist John Walvoord, Israel in Prophecy, p. 108)
Interesting, forgot about that one - and where in Zechariah is that found? I know it already, but it is also pertinent to this discussion. Is this a literal 2/3rds or spiritualized in some manner.