Maybe i should've been a little more clear. But keep in mind that I'm not talking about western countries outside of Europe. America, Canada, Australia have never been homogeneous besides the indigenous people obviously, but the current form of these countries was built on the premise of diversity. Homogenous countries were/are not.
But realistically diversity is not bad when done well. When it's incorporated at a steady pace where people can make it their own, you get wonderful results. But people are skeptical about the way it's being incorporated in the West today.
Specifically the sheer speed of it. Western European countries that are homogeneous or at least mostly homogeneous like Germany and France are having so much immigration that it's a shock to the system. These western countries can't adapt to or incorporate all these different cultures into their OWN culture fast enough to make it a melting pot and instead they're getting a salad bowl.
It's hard to argue against the social evidence that the way multiculturalism has been tried in the last 50 years has had many negatives in western Europe and the tensions are only rising. Even Japan is struggling with the reality that they might have to accept mass immigration due to their shrinking population.
The change is simply happening way too fast for these countries to adapt and others who see this are saying "we don't want that here".
i agree that immigration is a difficult thing to handle, and I think the best solution is to manage the amount that come in, and who comes in. Not to try to prevent change, or to counteract it. I agree its a shock to the system.
However, frankly part of the problem of destabilization of the West is a result of Western interference in politics elsewhere. The West has pushed the dominoes over the last century, and now its falling back upon the West. Change this, and things might be able to improve in the future. Islamic terrorism is a result of Western policies that destabilized Muslim countries, not Islam itself. People who are discontent with the West's role in the Middle East are using Islam as a tool in order to fight back. If we can understand that Islam itself is not the enemy, we can start working towards making everything work out (at least improve the situation, fixing it probably is very hopeful thinking). Part of that is understanding the West's role in bringing about the immigration crisis in the first place.