But working mums don't do what SAHP do, SAHP generally look after their children for much longer during the week, or at least those that work full time do.
Many working parents that I know aren't home until after 6pm, meaning they spend around 3 hours less per week day caring for their children (and that's ignoring before school clubs etc that many have to use). Then there's all the school holidays to consider.
Then, unless you're lucky enough to outsource a big chunk of domestic jobs, you have less quality time on evenings/weekends because all the things a SAHP does throughout the week still need to be done.
I plan to return to part time work when my youngest is 3. I'm lucky that this is a choice for me, and that it will allow us to save more for their future and provide a nicer lifestyle for them growing up, but I can't kid myself that I'm not sacrificing parenting time to do so.
OP, I think people judge because it makes them uncomfortable about their own parenting decisions. But people will judge whatever you decide to do, so you may as well do what works best for your family.