For example redistribution of wealth. Maybe we should do some of it, but people just don't see who expensive it is (and they seem to think "the people" will not pay these expensive costs)
There is a cost in the fact that giving money for free to people gives them the wrong incentives. Given enough wrong incentives, people will start doing things you do not want
There is a cost in that those who get that money often are not as good at using their money efficiently as those who are proven to be good at it by being wealthy
There is a cost in that wealthy people sometimes reinvest their money into services that benefit us all, which is lost if you take the money away from them