I think crying is fine - for communication wise, but am not too sure if its necessary leh.
Thats why i cannot agree with the article. And there are so many ways to keep our babies entertained these days, just the flipping part took my son's energy away man lol.
Just let him flip man, flip and flip soon very tired already, let him lie down on bed, on a/c, drawn the curtains make sure its super dark (i might be the first person to die of tunnel vision), on the white noise, give him the milk, - he drink till shiok will doze off one.
I think i read somewhere that if our babies have a good nap in the day, he'll have a good night rest too. Then no crying needed~ hopefully lah.