But you can't accept a contract just by visiting the site. Especially since the in the same action as becoming aware of the exist of the contract also makes you breach the contract.
> However I don't foresee any world arising in which the "the purpose of a user agent is to display me what I want to see and therefore any manipulation of the content other people own the rights to is within my rights" is going to hold up.
Why? This has always been the purpose of the user agent and it's difficult to impossible to actually make sure things will always look the same in all browsers. Could viewing a site in FireFox or Edge become illegal? Again, how would I know that _before_ taking the action. What about systems such as links2, w3m, elinks, and lynx?
> f you rewrite the terms of the contract, you have to account for the other side of the contract reacting to it, not just passively sitting back and going "Oh, gosh, I guess I'm stuck then, I'll just keep doing what I'm doing without changing anything."
Which terms? The UA has always been the agent of the user, not the site whose content is being displayed.
I just find it very difficult to believe that the court will accept that I've broken a "contract" I can't know exists without breaking it.
This is an assertion that is commonly made on the internet, but I see no reason to believe it carries any legal force, or even necessarily any moral force. In fact it's not that hard to read it as an argument made solely to come to the desired predetermined conclusion rather than any sort of principled argument. It implies that the sender loses all rights to anything they send to you, which is definitely legally untrue; I gave examples above already.
Also, if you win on this point, you will not experience a glorious utopia in which ad blocking is OK and you can save whatever streams you want and so on... you'll experience a world in which all this content gets removed from the web and locked behind even more proprietary clients that will come with what the publishers want. What may seem to you to be a simple bugbite back in favor of what you believe your rights to be may cause a much larger allergic response than you'd anticipate.
"I can't be sued for not watching commercials."
You haven't signed a contract saying you will. That may not be the case online.
The questions about whether such contracts should be something that even can be offered, or whether simply clicking through a EULA or accessing a bit of content can bind one to a contract, or the nature of what such a contract may be allowed to be, are all separate matters of interesting discussion. However I don't foresee any world arising in which the "the purpose of a user agent is to display me what I want to see and therefore any manipulation of the content other people own the rights to is within my rights" is going to hold up. There's too many rights and rights-holders that won't stand for it, and even if you did somehow win that case, they'll simply retreat and retrench in whatever it takes to recover those rights for themselves. If you rewrite the terms of the contract, you have to account for the other side of the contract reacting to it, not just passively sitting back and going "Oh, gosh, I guess I'm stuck then, I'll just keep doing what I'm doing without changing anything."