If websites are worried, why not just use TLS, which should prevent this sort of thing? This is not ABP, it is just an ISP being naughty (albeit in a way that its customers probably like).
I would explain to a non-technical person by analogy - imagine the telco needed you to use _their_ particular telephone when you make/recieve calls.
The Bell monopoly required you to not only use their handsets, you usually had to lease the phone from them.
It prevents the ISP from screwing around on their end.