One of the problems with the argument that nurseries are unnatural and therefore obviously worse for babies, is that there is absolutely zilch natural or traditional about isolating a woman in a house with a baby for 40 hours a week, and expecting the perfect nurturing environment for infants to result.
Communal societies, which ARE traditional, are not Nirvana either. The alpha famale is very likely to take her child's part and undermine/over-punish the others, and many parents find it hard to stand up to that every time, or even most of the time. I should know; I lived in one for a few years as a kid, and that was the main reason Mum decided to leave. I also had a child-minder after school for a couple of years who kept several kids in a tiny dining room for 2 hours after school with nothing but a table, chairs and a TV. Mum had little money and had to work - no choice back in the '80s - but to pretend that a childminder will always offer more personalised care than a nursery is ridiculous. It depends on the minder and the nursery.
There IS no ideal and perfect way to bring up a baby. I think my current situation - Mum living here, we get on wonderfully, she adores my baby and approves of how I bring him up - is as close as possible, but it's definitely infuriating to have your house rearranged in a way you dislike, your childrearing rules ignored when disagreed with, and zero privacy. Basically there's no perfect solution because nothing in this world is perfect, and screaming and shouting that there is, and it's your own, is mere self-validation at others' expense.
I do agree that good, solid research into what the effects are of various methods is called for, but actually I still think a good, loving nursery will be better than an angry, frustrated and/or depressed mother. Resentment and coldness from your mother is presumably more damaging for an infant than warm and affectionate daytime care, followed by loving attention from a parent who actually missed you.
The only debate that makes sense to me is, how can all nursery provision be pulled up to a level that is genuinely excellent? My neighbour sends her little girl to a parents' co-op. It costs the same as any other, but you also have to "bank" a few hours a month. You can do the accounts or IT or admin, cook the organic food, source and keep on top of suppliers and tradespeople, BE the tradespeople (they never need to pay a plumber!) fundraise... or work in the nursery. As a result there is always a parent around, as well as the paid staff, and the ratios are wonderful as that volunteer is not officially counted. The nursery is, unsurprisingly, brilliant and has a long waiting list, but as a model it strikes me as a really, really good one.