All adults need to work and people should only be a SAHP if both parents agree
I disagree with both of the above.
Adults should support or strive to support and care for their children.
Assuming you can do that on one income, there is no imperative for the other person to work. They can if they want to, or to meet agreed upon goals, but assuming the breadwinner has no plan or desire to cut back on their hours, they do not need to. If the breadwinner does want to cut back on hours, the non-breadwinner should pick up the slack if it is necessary to make ends meet.
I diagree that both people need to agree for one person to stay home. Person A should not have to go to work because Person B wants more money (not needs more money - wants more money).
My husband does not get more say in whether or not I go back to work than I do assuming we can make ends meet. His desire to have more money does not trump my desire to be home for the kids, make decent meals, volunteer, etc.
(fwiw, I do work part time, and my Dh agrees with me on the above - I am just using it as an exmapl,e)