Montegomongoose yes I would slam someone as ignornant and racist if they made offensive comments because they "hadn't travelled much" or "hadn't been exposed to multi-cultural Britain". By definition that's what they would be.
You would 'slam' them? Anyone, anywhere in the world, who was unused to seeing people if different ethnicity and commented on it?
Do you teach your children to 'slam' people with different views? Different life experiences? Different culture? Upbringing?
In my very humble opinion, it is 'slamming,' not listening, not conversing, that sets up one side as moral arbiter and the other as 'ignorant' that strangles meaningful dialogue at birth.
I have lived all over the world and encountered good and bad in people of all ages and colours.
I have lots of friendships which began with a discussion if differences and beliefs. Some changed over time, some did not, some are so deeply held that we choose to leave them put if our relationships (I think of a friend here whose homophobic views are, he says, a religious belief. I disagree. There is no 'slamming').
My great grandmother, on meeting my DH. For the first time, talked of 'white people' and what she thought of them. She came to love him. In your world, he would have 'slammed' her. They would both have missed put on a lovely relationship.