There are always exceptions – if you are writing about moves toward democracy in the Middle East, but you live in the US, you may need to be aware of how your context differs from those who live in the Middle East and that may affect your argument.
Purpose (aka intent) is a tricky thing.
I tell a joke – you don’t laugh. Is it more important that I want you to laugh or that you don’t laugh? Perhaps my intent to make you laugh and the fact that you don’t laugh are equally interesting to note, but neither is more important.
It is my not-so-humble opinion that one of the problems with education has been a focus on the importance of what the author meant (intent), when audience reaction is as important.
So – I prefer to refer to purpose as intended effect on audience.
There is purpose!
This is not to say there is no such thing as intent or purpose. When you are writing, you must know your purpose.