I would like to see shared care as a default position for all couples with children who live together.
Then shared care would also be a continuation of the status quo if those couples split.
However, where shared care is not being done when the couple live together, then it is completely unreasonabel to argue for shared care default poisition when the couple split. Children need stability and continuation of what they're used to and if one part of the couple hasn't invested as muhc time and emotional energy into the parenting of the children as the other has, but has actually benefitted from the free labour of the other person, by being enabled to earn more and prgress in their career at the expense of their partner's career, then it would be outrageous to reward that lack of investment in the care of the children, with joint care and control.
I have no problem whatsoever, with the notion of a default joint care and control of children, where shared parenting has actually genuinely taken place within the relationship while the relationship lasted. In fact, that's my ideal scenario. But at the moment, the lion's share of childcare, is still done by women and if men want 50 50 custody, then they need to step up to the mark and do 50 50 parenting while they're actually living with the mothers of their children. And if that happened, there'd be fewer divorces anyway IMO.