From libertarian Michael A. LaFerrara:
The Electoral College is part of the checks and balances designed to prevent concentrations of government power. For example, the United States Constitution supersedes the state constitutions, allowing the federal government to act as a check on states’ power. Likewise, since the elected legislatures of the states has the responsibility of choosing the electors “in such Manner as the Legislature thereof may direct,” the states can act as a check on federal power.
Also, the Electoral College acts as somewhat of a power balance between large and small states.
Likewise, the electoral college acts as a check on populism, which can be quite tyrannical. Instead of one huge national majority acting as a single overbearing power, candidates must win enough smaller majorities in individual states, each of whom may have differing interests, to accumulate the necessary electoral vote majority. The point is to check populist power as a means of limiting concentrations of government power;