From a health / genetics perspective it would be ideal if the parents did know who was the biological father of each child in case of future medical issues; but otherwise, a child being loved and raised by as many people as possible isn’t a bad thing at all.
And the “only thinking of their own wants / not a suitable environment to raise children / so selfish / children need a mother and a father / just wrong” was what society at large said, just a few short decades ago, in opposition to gay and lesbian couples wanting to adopt or use donors, and women who were single mothers by choice. Turns out we now accept they can be just as excellent as parents as married heterosexual couples. Why can’t polyamorous parents?