Today I've been adding all the siblings of my cousins' ancestor to Wikitree, going through Ancestry trees and using Wikitree X to quickly add them, then going back and adding actual sources. There are at least 11 kids in this family, and most of them grew to adulthood, married, and had children of their own, so this is a long-term project (especially since I'm not even related to them). I'm starting with just the 1850 census, so I have a long ways to go.
I came to sibling #8, Julia Ann Beeson Maudlin and no one had sources for her, so I looked at other Ancestry trees, and about half of them blithely replicated an error giving her the wrong husband, incorrect children, and even the wrong state of birth (Virginia, even though all of her siblings are born in Iowa or Indiana). Some people even gave her two incorrect husbands. Most have her dying in 1919, almost 50 years after her original death date in Colorado.
Even if I contact all of the people with inaccurate trees, it is unlikely that they will accept the correction. I will email one guy I've written to before because he's a direct descendant of one of the siblings.
It's the most depressing error yet that I've found in Ancestry trees. Life is too short to replicate errors en masse. Thank goodness for Wikitree.