Doctors hate it when people in a social setting ask them for opinions on their ailments. It isn't because they prefer you to go to their clinic so they can bill you, nor is it because they don't want to help. What people don't understand is, a clinical diagnosis is a well-informed weighing of probabilities. Doctors try their best, with all their years of gruelling training and whatever information they can obtain about you, to assess the most probable reason that you are unwell. But almost no diagnosis has a 100 per cent certainty.
They know full well the dangers of offering opinions willy-nilly and how they can be interpreted differently, depending on the recipient and circumstances. That is why opining on ailments is not something they would do lightly.