Article II: "The legislative authority of the state of Washington shall be vested in the legislature, consisting of a senate and house of representatives, which shall be called the legislature of the state of Washington"
That is the only clause in the constitution granting any kind of legislative powers at all, so therefore it's subject only to the limitations contained in that document.
In any case, it's not the job of federal courts to interpret state constitutions.
Using your logic, a State can bring back slavery. Is that really the amount of power you want to give your government? Even at a state level?