FYI "cry it out" is a form of sleep training to be done on a ~5-6 month old infant.
Any baby younger than that you basically should always attend to their needs and never let them cry without trying to soothe them [there can be a grey area from 3-5 months but still the general idea is the same].
Even a 5-6 month old must feel pretty unloved. Just put yourself in their position: can't walk, can't talk, can't get out of bed, feels tired, feels all alone, cries for help and comfort but is ultimately ignored.
That's the most worst message you can send out to a person of any age.
I often hear people say: but they learn, they manipulate you as if a baby’s personality was naturally hostile and their main reason in life was betraying their parents. :)
Any baby younger than that you basically should always attend to their needs and never let them cry without trying to soothe them [there can be a grey area from 3-5 months but still the general idea is the same].