Why can't i just be Jewish for ten minutes to get some ice cream? I can't think of a reason that is not also antisemitic. Motivation; We don't tell Jews they

Why can't i just be Jewish for ten minutes to get some ice cream? I can't think of a reason that is not also antisemitic. Motivation; We don't tell Jews they can only be Jewish if they have a reason we approve of. Time; no matter where you put the line, from a minute to generations, it would be intensely antisemitic to actually measure this and tell some subset of Jews they are not proper Jews. Synagogue attendance, circumcision, bloodline, race, all of these would be antisemitic some prejudice to actually test for or require. I'm left with the authors suggestion that the answer lies in the 'spirit of the law'. Which is just a nice way of saying 'what i think other people thought one time'. And about as subjective as it gets.