Only if you consider operator capacity as scarce as seats in an airplane

And if the airline can secretly put you on a Greyhound bus if they think you're flying too often.

Bandwidth is limited too.

Imagine everyone having unlimited internet data plans running torrent downloads 24x7 365 days a year.

I should start selling access to my wifi tether password at airports and other places where wifi is hard to come by.

Yes, but not for the reasons being brought up in the snide replies to your post. As with data plans, there are two types of people that snatch up unlimited deals: A.) Those who want to use a service at whatever pace meets their needs and not worry about running up the meter, and B.) Those who fly 16 round-trips to London in a 25-day span.