"We can still be friends" is a way for most people to ease their own conscience when breaking up with someone else. It's an easy out, if you go for it he doesnt have to feel like he's crushed your heart, and if you tell him to stick it he can feel like he made an effort. You have to be the one to decide if you still want him in your life
Personally: If someone disrespected me enough to dump me by text message I'd probably tell them where they could put their friendship.