Honest question for you -
is it considered insulting to Jews to make a distinction between Jewish ethnicity and religion?
I don’t know. Never been one to be easily insulted by anything.
A person is Jewish, per G-d, if his or her mother is Jewish or he or she had a proper conversion.
Are there lots of Jewish-by-G-d’s rules that don’t remotely follow His commands? Yep.
It’s just a fact. It’s nothing to be insulted by.
Me, as a religious Jewish person, worry immensely about such heretical Jews, not only for their own sake, but because I was taught that Jews were born specifically with a drive for the divine, as bringing G-d to the world is our job here on Earth as a people. If a Jewish person rejects that calling, that spark gets filled with nasty, nasty, things, and they tend to be very, very bad people (Bernie Madoff, Chuckie Shumer, whatever).