I've heard this response an awful lot, particularly to that awful 'being a SAHM is the hardest job in the world' advert. I have worked outside the home and been a SAHM and I do not feel that working meant I did all the parenting plus work on top. For example, as a SAHM parent I'd deal with squabbling, tantrums, discipline, naps, take them to parks/soft play etc and help them to play nicely with other children, cook with them, do painting and play doh and so on.
As a working parent I had an hour of getting them ready in the morning, dropped them off at childcare, then an hour of winding them down and putting them to bed at night. I could eat and go to the toilet in peace during the day, the house was tidy and needed little cleaning as we were rarely in it and I had very little to do with discipline etc.
I'm not trying to say working parents don't parent, because obviously they do but AIBU to think parents who work fulltime don't 'work and do all the parenting as well'? I don't get why working mums respond that way and think they're right but if a working husband came home and said to his stay at home wife that he does just as much parenting as her then I'm sure mumsnet would not agree.