But on the racism issue, it's not officially racist to ban travellers or gypsies, as these terms have been legally defined in the UK as people who choose a nomadic way of life, without reference to race or ethnicity.
So if you think your premises will get trashed, you are entitled to refuse entry to anyone you wish. I suspect the weak excuses for cancellations of bookings are because people aren't entirely sure if they're allowed to do so.