As implemented RSVP appears to mean "yes" but to many people RSVP (from French <<répondez s'il vous plaît>>) actually means "please respond."
As such people who intend NOT to come may send an RSVP.
I suggest either that RSVP be made more explicitly a yes, or that something like a yes/no radio button be added for more clarity.
Update: I'm going to move this conversation over to a newer suggestion. Allow Guests to RSVP to Event as "MAYBE" and "NO"
This is something we are considering but does not have a timeline at the moment.
However we are paying close attention to the most popular suggestions so please share and encourage others to follow and comment!