I'd be willing to flex a little and work a little longer to get more done short term for a cause, but if that became the new norm then I've just taken a pay cut

I'd be willing to flex a little and work a little longer to get more done short term for a cause, but if that became the new norm then I've just taken a pay cut and that's not an ok approach to it. A manager can always keep asking for more. That sounds like greed and costly employee turnover.