It is an index of extreme insecurity to want to keep someone away from their children. It is also a very nasty thing to do.
And quite wrong of the WAS to allow it.

The harm that the WAS does to the child can be repaired, and the relationship restored, but it takes time and effort on the part of the WAS. I try and stay out of it, since my kids are grown, although I encourage them to be kind to their father. They did not deserve this.

it also gives the lie to the MLCers argument that it is about the marriage and us. If it were, they would treat their kids better.