My 2 bob's worth.
Three basic categories of parents with wailing babes.
1. Aware of the possible nuisance to others, try their best to calm the infant. Usually obvious to other pax who will often then pitch in to help, if wanted; most.
2. Unaware of the nuisance, because its the usual 'background noise'. Will usually appreciate the situation with receipt of daggered looks or a first murmur from a FA; substantial minority
3. Couldn't care less. "Babe/infant has to know they don't rule the roost. I ignore wailings and to hell with the fact that we are in a small confined space with 50 others within earshot, for about 10 hours". These parents are the problem. Small minority, but most apparent. Should be on a 'no fly' list.