because without them, or customers, there is no company, no matter how many shareholders you have
Very true. But you can't have any employees or customers without shareholders - even if that is one person to start - because somebody needs to make the big gamble and invest the money to get a company started, then continue investing through multiple growth stages to the point where you could even go public.
One interesting point that many Slashdotters overlook is that post-IPO, "shareholders" don't exist for the benefit of the company per se - the buying and selling of a company's shares post-IPO puts no new money in the company's pocket (although share price does help with things like credit ratings, cost of capital, etc.). Having zillions of public shareholders is actually mostly to the benefit of the people who are or were part of the company and as a result were granted shares, be they founders, investors or employees. Without a liquid market for shares, they essentially are worth nothing (just ask someone like me who had a shitload of shares in a pre-IPO startup that were ultimately worth "1 shitload x 0 = 0") if you can't convert them to cash when you want to. Once your company is publicly traded, everyone who was granted shares in the company can either convert their "sweat equity" into actual cash, or see their investment rise or fall with the performance of the company as a whole.
It's no excuse for short-sighted profits-chasing on the part of some companies' executives, but overall being publicly traded has a lot of advantages for the people who actually worked to make the company successful (again, as long as they made sure to get an equity cut, however small).