Now, Senator John "seared, seared in my memory" Kerry: "If you put a tax cut into the hands of a business or family, there's no guarantee that they're going to invest that or invest it in America. They're free to go invest anywhere that they want if they choose to invest."
That's the attitude of the left: you can't be trusted to spend your own money, so we'll take it from you and spend it, because we know better than you do what you should do with it. Well, OK, that's the attitude of those on the left who actually believe their drivel. For the rest, it's a cynical exercise in buying people's votes, and hence power, by promising to steal other people's money to supposedly spend on them.
Discussion at greater length here.