But the truth is, that it is very hard to have a non multiculturalist view on the left without being branded by some with some very bad epithets. This is an example among many.

That's possibly because diversity (up to a point) is a left-ish principle, just as circling the wagons (and/or xenophobia) is a right-ish one.

But you can't really have discussions like this without defining terms and picking apart meanings. 'Immigration' is a mix of experiences and phenomena, some of which are deliberately managed and orchestrated, while others are spontaneous. There are historical motivations, economic motivations, political motivations, and personal motivations.

If there's a problem on some parts of the left it's a tendency to abstract these issues into tokenism to the point where moral positions become caricatured and drawn in crayon, so that whole swathes of the population - 'men', 'women', 'blacks', 'muslims' - have generically stereotyped and predictable relationships with other whole swathes.

Stereotyped relationships certainly happen sometimes, but they don't happen all of the time. Mistaking an individual for a social signifier of a stereotype is an abstract but not unpopular kind of personal abuse.

One giveaway is how people who live on the boundaries of stereotypes and are seen as neither one thing nor another have an unusually interesting time.