Neither the US constitution, nor does any commentary I'm aware of, state that electors are pledged to represent the interests of their state.
U.S. Constitution, Article II, Section 1, Clause 2: "Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors..."
The idea that a state legislature would choose electors that represent its interests should be common sense.
Of course, at every crucial point in history prior to the 1860s, somebody suggests reducing the power of states in favor of either democratic populism (Jackson) of federal power (Hamilton, Washington...), and the argument against goes something like, "You're just trying to abolish slavery!" American federalism was invented as a pretext to sustain slavery in the colonies where it was economically entrenched.
You could just as validly claim that slavery was a scapegoat excuse for the Federal government to usurp power from the states. Preserving states' rights is yet another reason why we would have been better off if slavery had never existed...