"Money doesn't buy you happiness" is a common catch-phrase used by members of the left. It is used to (supposedly) tell people that money is never ever going to make you happy.
I partially agree with that. Money, by itself, is a worthless material. However, this worthless material is currency in every nation in the world. Therefore, money can be used to buy goods, services, and probably most importantly when it comes to happiness, experiences.
So, because money can buy you these goods, services and experiences, it is a necessary, if worthless, material. You need money to travel the world. You need money to buy the beautiful house on the hill. You need money to do just about anything.
Because you need money to do these things that make us happy, money does actually buy us happiness.
Also, another stupid part of their argument is the belief that people in the Third World-people that literally live in cardboard boxes, eat off the ground, and have to walk a total of perhaps 20 miles a day just to get water for their families are just as happy, if not happier, than us in the Western World. Yet, it is the left that runs most of the campaigns for more aid to the Third World. How are they happy if they need money? The thing that doesn't help at all for getting a better life?
Therefore, the left contradicts their policies of aid to the Third World and welfare to the poor in the West when it makes this argument. They are only contradicting their other worthless policies and beliefs (it is well known that production, not aid and welfare, is better at getting the poor out of poverty, amongst many smart people. The left completely ignores this in their policies of aid and welfare).