The seminal works of Modigliani-Miller and Markowitz-Sharpe remain the cornerstone of financial theory. We reconcile these seemingly distinct approaches, in a unified theorem, by showing that the agents acting on the market defined by Modigliani-Miller are Markowitz rational when deriving the arbitrage reasoning in terms of Sharpe ratios. As a main policy implication, we show that government guarantees modify market's equilibrium as they provoke arbitrage opportunities.