Disfellowshipped people are supposed to be treated like "tax collectors and people of the nations". While such people might be looked down on for their actions, they were not totally cut off. Jesus himself associated with tax collectors (though he condemned some of their actions). They are, effectively, no longer members of the group.
The witlesses take that to the extreme. Not only is their membership dissolved, but they are harassed, often embarrassed (if they ever want to rejoin), and their families are busted up. None of that is scriptural.