Like any human organisation a union can be subverted by people who are into exploiting their members and doing well for themselves. It happens in churches, political parties, clubs, musical groups...

And that only happens because people let it happen and don't take responsibility for keeping things the way they are supposed to be, and changing them back to the way they used to be when they've gone wrong.

And of course you need unions - and in these times of fragmentation and short-term contracts and all that stuff which makes individual employees so vulnerable, you need them more than ever.