As a programmer, I know that DST (and time zones and durations and relative times) are all problems to be solved in the presentation layer. All business logic

As a programmer, I know that DST (and time zones and durations and relative times) are all problems to be solved in the presentation layer. All business logic uses well-engineered, heavily tested third party libraries for time arithmetic. All data storage keeps time zones with timestamps and durations. Anyone who argues that "I don't need to store timezones because all my dates are UTC" has a long and painfull learning curve ahead of them.