Risk parity is balancing the risk contribution of all asset classes (Stocks, bonds, commodities, currencies). With out levering up, investor portfolio will be 75% bonds and rest in other asset classes. So the expected return will be very low. If investor needs to some what similar to stock return, then they have to lever up the bonds. There is no other alternative. Investor can still make money (theoretically) since when bonds are not performing well, other asset classes makes up for it.