"In the situation where someone is a SAHM by choice, where the couple choose to split the childcare/money-earning in that manner, how is it that "one individual is able to dictate to another the manner in which she may live her life"?"
Plenty of women on MN who are SAHMs by choice are dictated to by their husbands about how they spend their day.
Despite having a full-time caring role they are expected to do all the housework because they are at home and not earning a wage.
In many cases they are not given full and equal access to household money. Many are given an allowance and the man keeps "his" money because he earned it.
There is a surprising number of women on here who maintain that a man should make decisions about how his wife spends her time if he's the only wage earner and that believe that his money is is own and if she's given any she's lucky.
That is a situation that women are choosing, in many cases because they expect to be treated decently and don't even see how unfair their set up is.
I believe you can be a SAHM and a feminist. But MN has really opened my eyes to how many women who SAH, especially those who are foolish enough to make themselves dependent on a man they are not married to, are extremely vulnerable to financial, emotional and physical abuse.
It's far harder to leave if someone else controls the purse strings.