It really has nothing to do with being able to support a stay-at-home parent or not. If you're bringing home 100k a year and quit your job to raise kids then the opportunity cost of having kids is 100k a year. The fact that you can afford to 'lose' that money doesn't change that.

Now you may think it's worth 'paying' 100k a year to gain all the non-monetary benefits of staying at home and raising kids, but that is a separate discussion.