No, its not rude to leave at intermission. At all. Leaving DURING the the show is rude.
Would you eat the meal at a restaurant if it didnt taste right? Would you wear a custom made dress if it was scratchy or ill fitting? No, you'd want it fixed. We don't have the option of that at the theater, our only recourse is to either suffer or leave.
I paid good money for a ticket, and if i choose to forgo part of the evening only has value to me.
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.