My contention is all of it. Here’s why:
Some people say they can split their attention on two or three different tasks at once. A quick logic check shows this to be impossible. If attention=100% of one’s brain, then splitting attention will result in a lower percentage spread over >1 task. It might be 99% of one's attention on an individual task and 1% on another, but the result of a split is always <100% attention. Therefore more than a single task cannot achieve one’s “full attention.” This is simple maths. I suggest the same reasoning can be applied to culture.
By definition, multiculturalism undermines the dominant culture because it divests concentration on one mode of thought and action onto other modes. In giving “equal time” for multiple cultures, the result is always an increase in "space" for the minority culture at the expense of the dominant culture which cedes "space." The greater the numbers of different cultures given “space,” the less there will be “space” for the dominant culture.
As the dominant culture recedes closer to 50% of total “space” the other cultures gain influence, fight between each other, until one (usually the more aggressive) secures a higher relative portion of influence to other minorities, before turning to and breaking down the failing dominant culture and finally taking power. For want of a better term, this can be called the Wedge Strategy.
This was one of the general goals of the Frankfurt School, and a specific goal of the Soviet Union against the West during the Cold War. In fact, the Soviets called progressives “useful idiots” because their agenda attempted the breakdown of Western culture from the inside. Multiculturalism is a major pillar of progressive thought.
I don't have a position on whether this is a good thing, simply that it is happening - and is the ultimate goal. If the result of this process is a reality our present society desires, then that’s fine with me. But let’s not kid ourselves it’s possible to share power when the central fact of humanity is groups will always desire more power.
A fear of losing key and secondary parts of Western culture (such as freedom of speech, freedom of assembly, women's rights, religious freedom, civil rights, gay rights, etc) is not the same thing as discrimination or refusing to help others in need.
Just using the immigration example, the narrative we are told is to let as many people in as desire to come to a particular country. Otherwise, we are somehow not assisting those people. But there are other ways to assist. For instance, consider that most of these people are leaving their home countries because they fall very low on Maslow's hierarchy of needs. A basic and non-controversial response would be to assist these people by ensuring their lives are improved while they remain in their home country. A second option would be accept those people for a limited time, work on restoring the person's home country, before finally sending those people back once the restoration is complete.
In other words, there is a big lie integral to the idea that not allowing unlimited refugees/immigrants/migrants, etc to enter a particular country is discriminatory. It's not. There are other ways to deal with the issue. In my view, a rules-based system is better than the opposite, and we have rules for immigration which protect both the refugee's culture and the entry country's culture, those rules should not be abused. Changing rules based on popular emotion triggered by manipulative media imagery makes a mockery of a rules-based order. This is not an ethical path.
Also, evolution tells us for every organism a change in allele frequency over time results in speciation. Put more simply, the gradual has the same ultimate effect as the sudden if both are cast in the same direction. So how does this map to immigration?
Well, >1 million new people from a diametrically opposite culture entering over a four month period a country of 80 million (Germany), coupled with a politically-driven multiculturalism that defers to those people in every social interaction, will accelerate the equivalent of allele frequency change in that society like oil on fire.
It may help to think of this coupling as the equivalent of a predatory mammal introduced to an island which has been home strictly to birds for 600,000 years. Case in point: New Zealand with cats, dogs and rodents (and people). A cascading series of natural selection events can change irreparably that island (culture) in a disturbingly short amount of time - in New Zealand's case hundreds of bird and tree species were wiped out within two generations, or c50 years.
What saved the rest of the New Zealand's birds? Human intervention and the establishment of a rules-based order which preferred (deferred to) birds over the predatory mammals. These examples aren't too far away from the results we might experience from mass migration.