I am not a parent. But if somebody is entitled, then it is the person that thinks that every public space should cater to their needs only. It’s a baby, they sometimes cry. You can’t do anything about it. What should the parents do? Never leave the house with the child, because its crying could annoy an adult?
Yes, it depends on the situation. A Movie Theater needs absolute silence during all of the movie, but a plane don’t. If the child doesn’t cry during the whole flight, I don’t see a problem with bringing them along.