Popa isn’t saying doctors aren’t good people. He isn’t saying they don’t love their mothers or that they watch TV on Shabbos when they’re not on call. I think the point he’s making is that it’s a lot more intrusive in frum life than other professions. You would have a home in which Dad goes to work every Shabbos; that’s a bit scary for child-raising even if it is mutar. Kids don’t understand these things so easily.
If someone is already a doctor and they want to become frum, nobody is saying they should stay out on account of their profession. But, if you are young and are thinking about med school, these are things to be considered. They shouldn’t just be sworn off even if someone’s uncle’s cousin’s friend DID manage to make it work.