In an adult, you mean?
A child is in the process of learning to behave, so I will always grant them a pass on not being able to listen and not being able to control their emotions/reaction. Not so much with any adult person, at least not with anyone who is also demanding to be considered an adult and treated like one. Being an adult is great, but it has a cost which is to stop behaving like a child ;)
I think there is nothing wrong when one decides to move abroad to be asked by the people welcoming them to not spit on what makes that country, well, a country where one wanted to move first.
Obviously, it all depends what the pledge is all about. If it means to respect, say, the Constitution, laws, and usage and maybe also show one has a basic knowledge of that new country too, that seems obvious to me. If it’s being required to shut the fuck up (not criticize anything), not so much.
edit: typos