Well right now we have a House of Representatives that is balanced by relative population, a Senate balances solely by equality of statehood, and an Electoral College with an elector population equal to that of a state's reps and senators. The TOTAL power of a state in electing the President is still determined by population, because more House reps = more electors, but by limiting the number of electors it ensures the RELATIVE power of each state is kept in check.
Switch to a pure democracy and suddenly New York, California, Texas, and Florida control the White House. My state of Montana? Alaska, Wyoming, Vermont, etc? Our opinions won't matter. We'll be forced to toe whatever line the Big 4 decide should be toed.