This is a topic very close to our family at the moment - and as this thread hasn't descended into silliness/insult swapping yet I thought I'd post my tuppence worth. I'm a sahm to our 18mo ds, partly through choice and partly because there are no jobs in my field at the moment. A field I spent nearly ten years training to qualify and haven't actually worked in (as a qualified) since having ds just after.
I also believe that ideally (and only when the parent wants to, because a depressed sahp is the worst option for any child, though I know some depressed parents have no other option but to be the main carer) babies and toddlers do best with a parent at home looking after them. That doesn't mean that wohp are doing wrong by their children - just that they're doing the best they can given the circumstances. As we all try to do. I was shocked at how many of my parent friends have had flexible working refused (I naively thought it was a right to have it, not just to request it) and think the attitude towards part time working is a massive part of our problem in this country. That and the culture of only women requesting it. I wholeheartedly agree with aldwick's early post, and was pleasantly surprised to see such sentiments expressed on this forum.
For me the main issue is not a need to feel validated for what I do as a sahm, but other people's attitude that looking after a child full time is 'opting out of work for a few years' (or words to that effect as posted by someone up thread). I am not opting out of working - I am doing a job I personally consider to be more important right now. And yes, some acknowledgment of that by the government would be nice.
I highly recommend a read of 'shattered' by Rebecca Asher. Lots of research about this very topic, and good coverage of the 'dads' aspect too.
As for me, I think I'll continue to look for work (pt) and am very fortunate to not financially need to at the moment (would be royally screwed if it was financially necessary) but I am very concerned about the effect of a long absence on my cv.