A legislator in California introduced a bill that would allow a family court judge the flexibility to recognize more than two parents for a child. Imagine what horrors await a state in which a divorced mother *and* her ex-husband's wife could both be parents to the children! Or one in which the biological father of a child could take custody of his offspring should the child's two mothers become incapacitated. Certainly no child has previously had parent-child relationships with more than two people before liberal legislators mandated it! (Because, as usual, adoption doesn't count as "real" when discussing families.)
Pretending that such relationships do not exist does not help families, nor children. It only forces the legal system to take actions which do not reflect the true state of affairs. Concerns such as "It's hard enough for children to be split up two ways, much less multiple ways" assumes a division between "real" parents and "fake" parents that may not exist as far as the parents and children involved are concerned.