If that's the reason they wash their chicken, they're more stupid than I thought.
I buy meat from the market, unpackaged, and only a handful of times I've had that slime on the chicken. The reason I remove it (don't need to wash it, just do it with the same knife I use to cut it) is because sometimes it can be reddish and it looks bad. I don't want to hear kids saying "maaaaa what's that red thing?? I don't want it...."
The "slime" ain't even slime, it's like a mucus. What is it? According to google, it can be either the result of adding raw chicken some (safe) additives to make it heavier, but it's more likely it's just normal residual tissue between the skin and muscle (reason why it can be reddish). The chicken was alive. Living beings have a lot of disgusting stuff. If you eat chicken with the skin, you don't really know what they have inside until you eat.
What a bunch of uneducated retards. I wasn't wrong when I said that they eat like children. "Agh, remove that thing I don't like" is what kids do.