My real sympathy for juggernaut started when he went solo against WW hulk powerless to defend Xavier. He may have hated chuck in the past but Xavier was such a jerk and even then Cain risked his neck to save him (I was rooting for hulk during that event, he has more common with the X men than the avengers), then he got the Cyttorak power and nearly defeated WWH but lost. In the end he told Xavier he hold no grudge against the X men but they'd better leave him alone for their own good. Since then he's been in villain until Yost rescued him and established as the juggernaut again, and holy Jesus in that arc he took down Colossus all by himself with no powers and then he somehow lost to him.
Juggernaut has the potential to be a reluctant ally to the X men just like Magneto and frenzy were