Big cities would rule the roost. Another check on power would be lost. Bad idea.
BTW, to all who care, Al Gore's "majority" popular vote can be ascribed to only Los Angeles and New York. Without huge majorities in those cities (forget about fraud for a moment) then Bush won the popular vote by 2,000,000.\
Consider that the next time your liberal friends whine about Gore winning in 2000. Should NYC and LA effectively determine election outcomes?