I spent 15 years in the mobile phone industry - working variously for big mobile operators, with phone manufacturers, and consulting with industry groups. I say this not to brag, but to let you know that I have experience with these matters.
Web browsers are often called a User Agent. They are a software agent acting on behalf of their user. So what happens when the browser acts against the interest of their user?
This isn't a theoretical question - there's a long history of browsers which betray the user.
Windows Phone 7 had a web browser that wouldn't let users download unprotected MP3s.
Symbian did something similar. If a file didn't have OMA compliant protection, the browser wouldn't open it. Deliberately ignoring the user.
In fact, Symbian went even further than that in disobeying instructions. Some Symbian phones wouldn't let you send an MP3 by Bluetooth or MMS. Why? Because the phone company didn't want to lose ringtone revenue. The customer of the phone manufacturer was not the end user; it was the phone network.
Blackberry's browser at one time had an artificial download limit of 3MB. No technical reason, just to stop users getting files from unofficial sources.
I'm going to keep banging on about this - the browser is the User's Agent. It is meant to work on behalf of the user. That's why you can change a page's style sheet, or block ads, or zoom in.
But the browser also has to protect the user. That's why you see warnings about entering your password on non-HTTPS sites. The User-Agent sometimes has to stop the user from doing something dangerous.
Can this be extended? Should the browser "protect" the user against non-DRM files?
Can you imagine that on every Soundcloud page? Or when sharing a video of your friends? Or on any media page without a © declaration?
Is this the future of browsers? Perhaps. Most browsers are made by media companies - or at least companies which make a lot of money selling audio and video content.
Does the browser work for the user, or the company that makes it?