In your rush to defend the actions of asshole bosses, you miss an important part: people who are trying to make a living with part time jobs are going to get another part time job. Not only are those people NOT more flexible than full time employees, but half the time they are less available than full time workers because they are stuck on a treadmill where not being at both jobs equals a loss in hours for the next week. There are tons of full time hourly employees who will JUMP at overtime.