I'm glad you have that opinion. I sense you may be being more limited in terminology that I. When I say Tribe Judah, I mean the remnents of the southern kingdom surviving today known as Jews, whether it be composed parts of Levites, Benjaminites or some members of other tribes that comprised the southern kingdom which was called the House of Judah.
I don't know; I didn't say anything about "stolen". My theory, howerever, since you ask, would be that believing as they do, that the term "Israelite" would be construed to mean only them, therefore not other Israelites, it could be seen as a form of theft. Hence the term "stolen".
Makes sense to me. Sort of like erasing someone elses name from a Will. Or skipping off with the contents of a joint bank account when the other parties were out of town.
If there is a group of Jewish people wanting to exclude everyone among the Israelites but tribe Judah from the Promises Of God as laid forth in the Abrahamic Covenant, they're on the fringe and their numbers are miniscule. The Falasha Jews of Ethiopia have been identified with Tribe Dan; Israeli Rabbis ruled in their favor and they were airlifted into Israel in 1991. They live as Israelis among the Jewish people today, and the Israeli government and an overwhelming majority of the Jewish people in Israel consider them to be bona fide Israelites and inheritors of God's promises to Israel.
Now: On the other hand, there's a growing number of people of Celtic origin clamoring for recognition as descendents of Jacob (most of whom claim to be descendents of Joseph), and the loudest and largest number among them disavow the modern-day Israelis' descendence from Jacob.
These cultists claim to be the true inheritors of God's promises and believe the modern-day Israelis are squatters on land they have no right to occupy.
This of course aligns them politically (whether they know it or not) with the Palestinian cause, and the arguments of Lost Tribalism constitute an apologetic for anti-semitism among those cultists who deny that the modern-day Jews are descended from Judah.
Lost Tribe theory is at the heart of much of the anti-semitism that exists in the world. That isn't to suggest that everyone espousing Lost Tribe theory is "anti-modern day Israeli," but if you run searches on the subject the results are overwhelmingly in that vein.