I think the objection in this thread to the whole 50/50 split is not whether or not it’s fair, but whether or not it’s realistic and doable.
There has to be a significant difference between a business contract such as the one you have described in the quotation above and a contract of marriage. If you remove emotion from a marital relationship, you may come close to a business agreement but is that really possible to do? And if you happen to arrive at an affirmative answer, then is it the right thing to do? What does removing compassion and emotion from a spousal relationship do to the quality of life that you anticipate?
Ultimately many of these questions only arise when breakdown occurs. Until then most average people are happy to ignore their contributions to the union and happily plug along.