To be fair JW's think they have Biblical backing for their shunning.
(Luke 10:30-32) 30 In reply Jesus said: “A disfellowshipped man was going from home to the grocery store and fell among robbers, who both stripped him and inflicted blows, and went off, leaving him half-dead. 31 Now, by coincidence, a certain elder was going down over that road, but, when he saw him, he went by on the opposite side. 32 Likewise, a pioneer also, when he got down to the place and saw him, went by on the opposite side."
Oh wait! Jesus ate with sinners, and never said anything like that!