If works for some and the families stay intact. With a mother and father. One size fits all doesn’t work with all families.
This is a strawman argument. No one ever said one size fits all with all families, not even God with the example par excellence The Holy Family. A Righteous Step-Father-protector, The Holy Virgin and the Son of God. Not the norm ever but our model.
But there are moral boundaries for male and female relationships created for a reason and when you play with these boundaries eventually it is going to cause damage usually to the most innocent involved