If you actually care about security maybe you shouldn't let information from the internet control your computer. I mean sure they can edit your webpages via a router to insert whatever, but the inserting whatever part is could just also be malware on the internet proper.
The point of TNO is that you might as well assume your router is altering webpages and inserting malicious content (either that or there's some already on the internet). One should view the internet as a black box of security threats and then just go from there. Yeah, routers can do that stuff. Security is what you do with that understanding. You don't get a router you can trust. You don't trust the router or the rest of the internet.