This goes on and on doesn't it?
People wheeling out various bits of 'research' - I think anyone with half a brain should realise that any of us can pick a few paragraphs out of various research documents and make them look as if they support any particular viewpoint, WOHM or SAHM.
Each to their own - as far as people have a choice. I think it's the people who don't have a choice, because they can't afford childcare so can't remain in employment, or can't afford to give up and are stuck in a job they don't like.
I also think there can be a tendency among a lot of people to be slightly disingenuous when it comes to the reasons for making a decision. For example, a lot of the people I know who gave up work completely when they had kids, either weren't enjoying their job, weren't doing very well in it, didn't earn very much or didn't have good prospects. Not all, but a lot. Therefore, it's hardly completely honest to say they were giving up because they thought it was the best thing for their children. It was what they wanted, because they wanted to be at home and not work. Conversely, most of the people I know who remained in work, enjoyed their job and had good prospects. Makes sense really!
As someone else said, you won't be able to tell which children have been in nursery or with a childminder a few years down the line - you also won't know whether your child will thank you for staying at home or not! My own mother was a SAHM (but then that was far more common in her generation) but I can't honestly say hand on heart that it was the 'best' thing for us kids. I didn't know any different. Maybe it would have been just as good if she'd worked!