"Economists are generally concerned about the rising MPS in an economy." Explain why?

Rising MPS means that consumers are saving a larger part of their additional income. 
we know MPS + MPC = 1
hence an increase in the saving of additional income will lead to a fall in consumption in the economy. MPC will start falling. When the economy starts consuming less then AD will fall. The fall in AD will cause a fall in national income and multiplier. There will be deficient demand and the new equilibrium level of income fall. This will lead to unemployment as the producers will start reducing production and the economy will start moving towards deflation.