You do NOT think its possible for babies to be obnoxious? Seriously?
As far as the parents thinking it is cute, I have no other explanation for parents who subject their noisy little brat upon others.
If our children cried inconsolably, we had the decency to remove them from whatever situation we were in: restaurants, stores, social gatherings, whatever it was. Again, I understand its a plane and during takeoffs and landings there's little that can be done, but in general, in other situations, yeah, we leave with the child.
I expect no less from others.