An entrepreneur who creates a business does useful work. Someone who investigates businesses to see which deserve capital invested in them does useful work. However, the person who just sits back and earns a living off interest, or plays all day buying and selling stocks is not producing anything useful. He is just engaging in respectable form of gambling. These people are little better than welfare bums in terms of the way they are investing their time .
Profit becomes the only motive for business decisions.
This leads us as a species to do some very odd things. For example, we as a species have now developed the technology to totally wipe out the AIDS plague. However, we refuse to use it, because our capitalist mentality insists that every person taking a medication must pay equally for it. It does not matter that the cost would be trivial to produce the medication to wipe out the plague now that the difficult work of developing the drugs has been done. Further, we don't wipe out AIDS because that would be unprofitable.