The big problem with more money flowing in the economy is this;

It removes the productivity that we created.

If the money supply is fix, then prices go down because everything is easier to put our hands on.

On the opposite side, if the money supply increases more than the rate of our productivity, prices go up, because there is more money trying to buy the same amount of goods.

Think of rare collectibles (the rarest item are always more valuable, they also lose value if more of them are being produced)