I think dentists often keep short hours because they like them.

Plenty of other businesses do hire lots of part time people and manage their hours in order to avoid obligations. If you don't think that is true, well, I don't even know where to start.

Its hardly a brazen accusation. He said "I believe" and then made a fairly innocuous statement. Relax. Even still, just because your dentist is open 43 hours it does not disqualify his statement.

Accusing people of being ‘uncompassionate’ on zero evidence is not exactly innocuous - it’s sadly common on the internet, but it’s still a pretty jerk move.