This is as touchy as false allegations.
It's debated and of course in some circles poopooed.
Whether it could be argued as an actual mental problem, there have been numerous instances of a parent, usually the custodial parent, causing a rift in relations for the noncustodial parent and actual alienation with a child or children.
Are there real allegations of abuse? Damn skippy there are, too many. One is too many to borrow the lib broken record.
But there are far too many instances where, out of spite, jealousy or other reasons, one parent is villainized when there is no reason. The damage is not irreversable and when I get my Ph.D in Psych eventually, I would endeavor to help these kids to come to grips and rise above the hurt.
There is a lot of healing needed to be done for so many reasons. It's part of reconstructing the deconstruct.
If face for any reason, always dig for info. find out what's legit and isn't.
Honesty is the best policy.
Trust, hard earned, is the goal.