Canada

Didn't think I'd see support for Citizens United here, but I guess anything is possible...

Anyway, publicly traded corporations are subject to incentive structures that the market has created. Corporations are run by a CEO, but the CEO is elected by the board. The board, in turn, is elected by the shareholders. The shareholders are mostly mutual funds, which are funded by ordinary people.

If the CEO makes decisions which clearly reduce profitability, then they will be fired by the board. If the board doesn't fire them, then the mutual fund managers will vote to replace the board. If the mutual funds don't replace the board members, their funds won't beat the market, and their investors will pull out and put their money elsewhere. And if none of them do any of that then another grocery store will raise prices as much as demand allows, increasing profits relative to the more "noble" grocery corporation, which will allow them to take on an influx of investment capital which they can then use to expand their market share and gain a competitive advantage over the their competition.

So ultimately, the "greedy" one is Bob, a middle manager in a nondescript office park in suburban Iowa who wants to invest his retirement funds somewhere with good returns so that he doesn't have to work until the day he dies.

This is why Citizens United was a bad thing. It expanded the ability of inhuman, profit-maximizing machines to influence politics.