You know what you're buying. You're buying a share of the earnings/monetary value of the company, and are valuing it based on your belief in zuck as a leader. You are not buying any control in the company, and that's pruiced in. I'm sure shares would be worth more if zuck didn't control the company and you could gain control by buying shares.
So in the best interrest of shareholders, if you believe that shares would be worth more, if they they didnt have this class segregation, then they shouldn't..
Zuckerberg would argue that even if shirt term the value if the stock is lower, his judgement abilities are superior to that of the shareholders, and that it is better for the shareholders if he maintains control. He is also a shareholder after all, and he's doing what he believes will optimize the value of the shares since that is what he's encouraged to do. And who cares if it's in the best interest of shareholders? Shareholders know what they bought. They bought a share of the earnings generated by a company fully controlled by Zuckerberg. If they bought it, then they are fine with these terms. And zuck is clearly happy with things the way they are. If shareholders dont think zuck is maximizing their value, they dont have to own his shares, and if people cared and sold, that would incentivize zuck to change things.