Please access the above link to know the context of discussion.
Why Jews are Called Jews
Ben Masada the Executive Member of the above site has stated that the
reason as to why Jews are called Jews is that they come from the Tribe of Judah who as per his statement is all based on God’s promise to David that his Tribe (of Judah) would remain as a lamp in Jerusalem forever. (I Kings 11:36).
Was not Judah involved in the conspiracy to sell Joseph as a slave?
Morally it is wrong to say that Abraham was a Jew or Jewish.
The Hebrew name for Judah, Yehudah (יהודה), literally “thanksgiving” or “praise,” is the noun form of the root Y-D-H (ידה), “to thank” or “to praise.” His birth is recorded at Gen. 29:35; upon his birth, Leah exclaims, “This time I will praise the Lord,” with the Hebrew word for “I will praise,” ‘odeh (אודה) sharing the same root asYehudah.
Judah is the fourth son of the patriarch Jacob and his first wife, Leah: his full brothers are Reuben, Simeon and Levi (all older), and Issachar and Zebulun (younger), and he has six half-brothers.
Following his birth, Judah’s next appearance is in Gen 37, when he and his brothers cast Joseph into a pit out of jealousy after Joseph approaches them while they are working in the field flaunting a coat of many colors. It is Judah who spots a caravan of Ishmaelites coming towards on the way to Egypt and suggests that Joseph be sold to the Ishmaelites rather than killed. (Gen. 37:26-28, “What profit is it if we slay our brother and conceal his blood? … Let not our hand be upon him, for he is our brother, our flesh.”)
Judah marries the daughter of Shua, a Canaanite. Genesis chapter 38 Judah and his wife have three children, Er, Onan, and Shelah. Er marries Tamar, but God kills him because he “was wicked in the sight of the Lord” (Gen. 38:7). Tamar becomes Onan’s wife in accordance with custom, but he too is killed after he refuses to father children for his older brother’s childless widow, and spills his seed instead. Although Tamar should have married Shelah, the remaining brother, Judah did not consent, and in response Tamar deceives Judah into having intercourse with her by pretending to be a prostitute. When Judah discovers that Tamar is pregnant he prepares to have her killed, but recants and confesses when he finds out that he is the father (Gen. 38:24-26).
Meanwhile, Joseph rises to a position of power in Egypt. Twenty years after being betrayed, he meets his brothers again without them recognizing him. The youngest brother, Benjamin, who has remained in Canaan with Jacob, initially remains in Canaan, so Joseph takes Simeon hostage and insists that the brothers return with Benjamin. Judah offers himself to Jacob as surety for Benjamin’s safety, and manages to persuade Jacob to let them take Benjamin to Egypt. When the brothers return, Joseph tests them by demanding the enslavement of Benjamin. Judah pleads for Benjamin’s life, and Joseph reveals his true identity.