[jimmaswell]

I'd consider Twitter a successful big competitor to Facebook in terms of social media. They're not 1:1 in features but they're public social media spaces meant to make posts, find people, have a profile about yourself, somewhere cited by mainstream news and everybody has heard of. Facebook use is declining last I heard anyway while Twitter rises.

[harry8]

You can always claim any monopoly is not a monopoly by defining the market to be larger. Google tried to do a facebook competitor and failed, abysmally. The end. Twitter is not "a different facebook" and the idea that it could be is ridiculous outside of discussion of monopoly.

"Water distribution is not a monopoly because you can go to your local shop and buy a can of coke or a bottle of artisan spring water if you're thirsty." Every monopoly always makes an argument like this. Treating it with withering contempt is always the correct response to such nonsense. Your family "christmas letter" or equivalent relating to more distant friends and relatives family news is also not a competitor to facebook despite some similarities. So it goes.

You cannot do what facebook does in competition to facebook at any price. You can't get whatever people get from facebook somewhere else at any price. That is market power. That is what economists call "market failure." That is an open-and-shut case for regulation the same as electricity and water distribution on the grounds of natural monopoly. It's so open-and-shut that's true whether you lean socialist, libertarian or something more moderate.

[jimmaswell]

What is your definition of the service Facebook is a monopoly of?

[harry8]

Exactly. Well illustrated, thank you.

One can play definition games all flipping day long and turn it into a poor quality highschool debate. Monopolists always attempt this in defence.

Whatever the correct definition is it has the same definition as google's attempt to do the same thing where it poured a multitude of resources and expertise into it and failed while facebook made billions in revenue.

No definitional games alter that fact. As long as the definition captures /that/ it's fine, but wholly unnecessary. And you can mess with definitions and have defintion debates in quagmire as long as you choose which is what every single monopolist wants and will pay lobbyists, lawyers and politicians to achieve that end to prevent the obvious and necessary action.