If you're talking about Google Calendar it isn't possible at this time. I feel you though and the reason I know it can't be done is because like you I'm guessing you noticed all the latest crazy holidays listed on your calendar, most for some made up crap, but I digress. Like you I went looking for a way to remove this offensive crap only to find it's all or nothing. Isn't that nice. You will observe or you can get nothing. I currently can't give up Google Calendar, perhaps you can, if so go to the Play Store and start shopping. Someone has to put out a calendar that doesn't try to indoctrinate everyone.
Keep the faith
Best wishes