Common emotional blackmail
Using love as leverage to double-bind children to obey—threatening to withdraw the relationship—is wrong. Children have a right to our love.
economic dependence
That something is legal does not make it right or best
An argument that the mere fact that something is legal does not make it right or best. Many different things are perfectly legal; not all of them are good.
Why allow minors to disregard the guidance of their elders?
Does financial supporting our children mean they must obey us? Is it right to expect quid pro quo for our support?