usually used more before a decision - like, i considered going to the zoo, but decided not to.
but now i am a little bit in doubt about whether my perspective is surely right (whether it is helpful or not for everyone).
but now i am a little bit in doubt about whether my perspective is definitely right (whether it is helpful for everyone or not for everyone).
if 'for everyone' comes after 'not', to me, it sounds like 'whether it is helpful or whether it is not for everyone' - that is to say, 'whether it is not something everyone likes', which i don't think is what you mean! that was a 