Mine was happiest when cuddled, blissful contented baby when snuggled, desperate and howling when not.
For him, there wasnt any option of any gentle sleep training, he was utterly bereft and clearly couldn't cope when left without human contact, lying on his back in a cot for example.
But all babies are not the same, and I think perhaps this is the issue behind some of the dissent on here. If anyone tried to sleep train DSit would have broken him and been an incredibly cruel thing to do. But, other babies are totally different. For example, the idea of laying down a sleepy calm DS and him whining a little but in a grumpy way that fades into sleep/ calmness again... that would never have happened with DS. So for me, that shows that a baby who will grizzle and acquiesce is a whole different beast to the type of baby DS was. And putting that baby down for a little while would be good parenting, no issue.
I wonder if that's why for some people leaving a baby without human touch conjures up horrific scenes (as for my little squishy limpet DS!), but for others the whole 'baby wearing' as necessity conjures up ridiculous lentil weaving overkill (cushioning a baby who's not that fussed being strapped on the whole time etc).
I think the lesson is, baby's can be so, so, different. And although every baby needs secure attachment and plenty of human contact, one baby's needs will be satisfied in different ways from another.
I'm very glad we've moved on from the days when attachment wasn't considered important at all, that causes untold harm. My mother was told not to pick newborn me up except for feeding/changing as it would 'disturb' the baby. My mother adopted this mantra with enthusiasm (it fitted with her overall warped view of people), and from my earliest memories til today there isn't a bond with her at all. I still deal with the damage her lack of love caused.
But that damage is not caused by a few minutes in a cot when the baby's not actually distressed, and I think we need to remember that.