Another happy, fulfilled SAHM here.
I never had a career, though. I've known for a long time that I WANTED to be a SAHM, this despite my "feminist" mom trying to convince me that I should be a diplomat or something.
My kids are all in school now, but I still stay home. I "justify it" by knowing that on teacher in service days, snow days, sick days, etc. I don't have to scramble for child care. I just love on the first snow day of each year, watching the news stories about all the parents grumbling that they had to leave work early to pick up their kids for the early snow closing.
Also, I do a lot of volunteer work in the schools. A LOT of programs/events/etc. happen in school because of SAH parents volunteering.