“The problem with Jews for J is what he did by leaving.”
What does this even mean? Left what? He never stopped identifying as a Jew. Christianity wasn’t spread to the goyim until Paul. It started out as a sect within Judaism that was considered heretical. Were you under the impression that chazal added the birkas haminim to refer only to non-Jewish religions?
How people self-identify is completely meaningless. The Essenes, Tzadokim, Early Christians all identified as Jews (and halachically were). Ironically, the only group who’s name implies an act of leaving or separating was the Perushim.
“I think you misunderstood my position.”
Would you eat the food of a polytheist who still identifies and acts as Jewish? Your opinion seems to be that unless there is some official “leaving Judaism” ceremony, then everyone is still considered fine.