I don't find being a SAHP mind numbing in the slightest and I agree it has absolutely nothing to do with intelligence , that would just be insulting assumption.
I love it, spending all day with him, for me it's time I will never get back so I made that choice. I feel very lucky we live where I had that choice wether to go back or not.
I chose to be a SAHP as I didn't want to drop my child off at 08.30 and pick the up at 16.30 and be dashing around to get everything done and I personally would have felt like I was missing out on the majority of their day throughout the week, and just always being rushed (as would have been my case) and in return for that choice I had taken time out of my profession with the hope of returning when he starts schools, the risk I took was at what level. That's the trade off. You normally can't do both and you don't have to, that's ok, both are viable options, you just choose which one is best for you and your family.
I personally can't understand this "not having anything to talk about, or any adult conversation" view as I never used to really talk about work anyway when we socialised. As no one knew who I was talking about and my job was really interesting to me and I loved it, but my friends don't, so we would do a 15 min rundown each if something major happened or funny.
As a SAHM you can absolutely keep up to speed with whatever you like, read the current research in the subjects you are interested in, do night time uni or distance learning, courses that keep you relevant in your profession. They are not any less of a contributor in their relationships.
I also understand women who want to get back to work, they have worked hard to earn the position in their firm, or they just simply prefer working out of the home. They are not any less of a parent.
Everyone is different and that's a great thing, people should just do what makes them happy and screw any judgy people or those who are offended by your experience, they are normally the ones who are quite unhappy with their choices in their lives, so be kind to them.