Have been both SAHM, and WOHM - When DD1 was young, i had a full time job and/or full time university course/PhD. This was much easier, i feel than being a full time SAHM - because my parents looked after DD1 for me, i never had to worry about school holidays, pick ups etc etc. So just did my work, came home, picked up DD at no set time, sometimes my parents had given her tea.
With DD2 i don't have that luxury and have found the whole work/childcare balance too much, not just the childcare, the everything else that became easier for me when i had someone else to "do the parenting" for me. So compared to being SAHM, far more stressfull and exhausting.
So for me it was a scale of "toughness"
WOHM with grandparents to do childcare (piece of piss) - Full time SAHM (can be a bit monotonous, and being chief entertainments officer is knackering) - WOHM without grandparents and having to juggle after school club/ pick ups, holidays and DPs working times etc, (too much for me!)
I think it really depends on who you are, what your job is, what childcare arrangements you have etc.
Being a SAHM is not a job, it is however bloody important - being a SAHM is no better than being a WOHM
Why is this even a debate