That's rather odd, freedom of speech and all that. You can talk about anything you wish doesn't give them the right to ban you.
I thought you are in the UK, your flag is for Scotland. The UK does not have freedom of speech, there are a lot of laws that limit what you can say. The UK is so restrictive now that people from other countries are coming here to use the British laws to sue people for libel.
Also, in the UK at least, a shop manager can ban anyone at any time for any reason or no reason. They are not obliged to allow anyone onto the premises that they don't like, and can sue for trespass if someone that has been banned enters the store. The only exception is if the reason for the banning is to do with race or sexuality.
All that is important is known.