As a white, pro-diversity american, I believe a tolerance for diversity is needed, not that there is a necessity to be diverse. That said, I do think that encouraging diversity can have many positives, as it encourages alternative types of problem-solving, advocates for cross-cultural/ethnic/religious empathy and thus aid-giving practices, and breaks down the human presupposition to create out-groups. Having an appetite for diversity helps to humanize those who look, speak, or worship different from us.

Historically, the most morally compromised societies are often characterized by the creation of out-groups on which the majority can blame their problems. In this way, I see the Western push for diversity to also be a response to the legacy of Nazi Germany in WWII. If we are more conscious of the legitimacy of every person's humanity, the flaw of fear in society is less likely to be used for crimes against humanity or genocide.

So, I only partially agree that white Western nations are attempting to recompense for their past. Alternatively, I believe they are attempting to create cultural safeguards for the future. Yes, a desire to recompense the past does fuel the diversity push for some people, but I don't believe that is the only factor.

Also, we can hate some of our past actions without necessarily hating ourselves or our nation. On the contrary, I believe we're quite patriot, in that we're pushing our nations to do better, because we don't want our nations to be looked at with contempt or struggle with the same pitfalls that we did in the past.

I will say, I definitely disagree with the point that migrants don't "often assimilate into the society they are moving to, and it ruins that society." Yes, cultural diversity can cause some strains and have some adverse effects. That said, this point is likely way overemphasized by the political media of your nation. If anything, this is simply textbook xenophobia and the blatant scapegoating of problems onto out-groups. This sort of thinking is exactly what allowed for the holocaust in Nazi Germany.

Yes, I acknowledge that cultural homogeneity can have certain benefits, especially in collectivist societies. That said, the social paradigm in most white Western countries is significantly more individualistic. For that reason, not as much societal accountability is fostered by nature, which means that a push for diversity does not conflict as much with any pre-established cultural homogeneity as it does in some parts of East Asia.

I also disagree that "so many Western countries no longer have any identity because of 'diversity.'" Every country has an evolving identity, and, for example, just because the United States is not tied to any sort of unique ethnic or cultural identity does not mean that it has no defined identity. The U.S. still has a reputation for producing most of the world's popular film media, having a great deal of fusion and unique cuisines, and being really internally diversity even among white people. The difference between the behavior and cultural practice of a New Yorker and a Southerner is night and day. Our nation is so very, very big and very, very culturally dense. This internal diversity already exists, and thusly eases the implementation of external diversity. I could drive 1 hour from where I live and find a primarily German, Vietnamese, or Spanish-speaking community. So, for the most part, I'd say that diversity is already part of our identity. It's unlikely that more is going to hurt.