> That still breaks the experience. Now you have tampered content AND broken clients.
You won't have tampered content if the data is rejected, that's absurd. You can do the same with TLS by the way, that's the whole point of TLS, being able to verify (and thus reject or not) data.
Sure it break the client, but you can do that in any situation, just have to unplug a wire ;).
TLS does wonders for preventing transparent proxies, DPI & ISPs from modifying or tracking what you see.