Earlier quoted context omitted.
You still wont be able to break the end to end encryption of a site. You can only intercept traffic that the server can read, you can't intercept traffic that are encrypted end to end. And if the site can see your data assume the government can see it as well, they can get it with a warrant.
Website-based end-to-end encryption isn't usually. In most cases, the "e2e-encrypting" website will deliver the Javascript that does the "e2e-encryption", which can easily be manipulated to provide a copy of all messages to some convenient third location. A warrant will maybe warn the site and the user that something is going on. A man-in-the-middle attack without a warrant delivered to either party is more likely to…
Updating others javascript as a proxy isn't "easily".
Also if the government goes all this way to tell each internet provider to spy on people, why do you think they couldn't tell certificate authorities to spy on people? It is the same level. I wouldn't be surprised if many CA's in USA already does this.