A tyrant is a dictator who rules without regard to popular opinion. Thus there can be no such thing as democratic tyranny. The danger of direct democracy is mob rule, not tyranny. There is no mob rule in referendums, since things are not decided in the passion of a moment, but take a long time and are subject to normal democratic debate. Also as I already explained, the rule of the majority is not unchecked, and the majority of state costitutions are not flawed just because they can be easily amended. A state constitution does not serve the same function as the federal one, most state constitutions are huge and deal with everything including the kitchen sink.