A better way is for you to define Holidays as individual date based events with time transparency set to TRANSPARENT, rather than OPAQUE.
Alternately, you could set them to OPAQUE, but give them a low PRIORITY compared to normal group scheduled events (i.e., CATEGORIES:MEETING).
A still better approach is for a calendar for the user to have a robust "user profile" that allows you to set that you allow or don't allow scheduling of events and to-dos on Holidays.
-- Frank