My ISP is well known for using Deep Packet Inspection techniques to look at what you're doing and where, and to shape traffic to sites they want to discourage -- like NetFlix. And they inject their own ads into web pages, which could be a source of malware. It's trivial for large providers to get root certs so that they can MITM any TLS traffic on their network, unless you're using pinned certificates.
So, I need to protect myself against my ISP.
And their name? AT&T.