I find it rude because if I emailed them, it might be an FYI but requiring no action. If they just delete it, they might then be confused about project status later. I would be annoyed to have to re-send a message after the fact because they don’t think ANY email during their time off has value.
I hate when senders ignore the instructions in my OOO message. Usually, my message is something simple like: “I am out [Dates], returning to the office [Date]. Please contact Jane (jane’s email address) in my absence. General [department] questions may be sent to [general dept email address].” To me that says if you are sending me anything then I won’t see it until I return. If you have something you need to be resolved right away, you can contact Jane or send it to our department inbox (where it should be going anyway).

Front makes it easy to save vacation responders and turn them on and off. If you're not on Front (yet!) here's how to save one in Gmail or Outlook. Then just copy your message into your vacation responder, rest assured your emails will get a response, and hit that glorious "Sign out" button.
Our factory and office will be closed from [date] for Celebrating [holiday name]. I hope this holiday will more enjoyable and give you more time to be with your family. All your inquiry will be attended to once we resume normal operation on [date]