what would it be like to not have the illusion of free will ?

beautiful question
sounds paradoxical!

the illusion of free will is basically a way to hide behind certain realities are not in sync with your perceptions or expectation of life.

when certain things do not happen in a way you want them to, you sort of console yourself putting different arguments, this is often referred to as Self defense.
one of the strongest argument used here is the free will argument.

as far as I understand, if we did not have the illusion of free will, behind which we hide and give excuses for not achieving things.
we would come up with another argument which gives us excuses to hide behind.
because we as human beings dont like to stay with things that are unsettling or things that do not have an answer

also when there is anything unsettling or anything that does not match with our perceptions or expectations we seek to such arguments.