It depends what you mean by “disillusioned.
Let’s start with the word “illusion”. What does it mean?
One if the meanings according to Professor Google is that it is “a false idea or belief”.
Taking this as the definition, it follows that if you are under a an illusion, you believe something which is false.
For example you may believe that the moon is made of cheese. We can safely say you are under a delusion.
If you go to the moon (compliments of NASA) and find out that the moon is not made of cheese, your false belief is gone. You have been disillusioned. You are no longer deluded.
So, becoming disillusioned is a good thing!
These days people believe plenty of things that are false.