Once upon a time, it was possible to view the Internet as a generally benevolent place as far as your traffic was concerned. Both passive eavesdroppers and man in the middle attacks were uncommon and took generally aggressive attackers to achieve (although it could be done). Eavesdropping attacks were things you mostly worried about on (public) wifi or unusual environments like conference networks.

I am afraid that those days are long over now. On the modern Internet, ISPs themselves are one of your threats (both your ISP and other people's ISPs). ISPs routinely monitor traffic, intercept traffic, modify traffic on the fly both for outgoing requests (eg) and for incoming replies from web servers ('helpfully' injecting hostile JavaScript and HTML into pages is now commonplace), and do other malfeasance. To a certain extent this is more common on mobile Internet than on good old fashioned fixed Internet, but this is not particularly reassuring; an increasing amount of traffic is from mobile devices, and ISPs are or will be adding this sort of stuff to fixed Internet as well because it makes them more money and they like cash.

(See for example the catalog of evil things various ISPs are doing laid out in We're Deprecating HTTP And It's Going To Be Okay (via). Your ISP is no longer your friend.)

The only remedy that the Internet has for this today is strong encryption, with enough source authentication that ISPs cannot shove themselves in the middle without drastic actions. This is fundamentally why it's time for HTTP-only software to die; the modern Internet strongly calls for HTTPS.

This is a fundamental change in the Internet and not a welcome one. But reality is what it is and we get to deal with the Internet we have, not the Internet we used to have and we'd like to still have. And when we're building things that will be used on today's Internet it behooves us to understand what sort of a place we're really dealing with and work accordingly, not cling to a romantic image from the past of a friendlier place.

(If we do nothing and keep naively building for a nicer Internet that no longer exists, it's only going to get worse.)