"Using it productively" (i.e. investing) is ultimately just taking from someone else's salary. Outside of minting, money is a zero sum game. The laborers in the company produce labor and goods, the company (and, by extension, the investors) skim labor off the top. They are stealing the money which rightfully belongs to the workers by using other money. They, who have the least need, are given the most.
That's just irrational... Without the corporations, where exactly do you suppose people would work? Comintern? The investors put their money in and hope to reap rewards... What they do is risky; its just a form of gambling. Do you think that should be illegal too? Or, for that matter, anything other than being a factory worker?