First off, I'm human and imperfect, so I'm not saying I have all the answers.
The initial question I replied to was "do whites belong in Africa?" My response is that question is immaterial. We are a migratory species, so groups moving to new areas for better opportunities is just part of our nature, and part of how we became who we are. I don't think you can say that fact, in and of itself, is "good" or "bad".
I see problems when the groups that migrate do not contribute to the overall success of the areas they migrate to. In my examples, I would say that the Chinese migration to the US was a net positive for the US. They have, as a group, contributed back to the society they came to.
In the case of say, Syrian migration to Europe? I don't know. I don't live there. It seems to me, based on what I can see, that it is not going well. Can it be improved? Again, I don't know. But I would say my measure would be this- what will the Syrians provide BACK to Germany that will be a net benefit to ALL Germans, including the Syrian migrants. If their main contribution is to transfer the undesirable aspects of their culture to Germany, I would say it is BAD. But it's always a mixed bag, and maybe too soon to tell.
I live in Southern California, and I think that this area is one of the best places in the world specifically because it is a destination for people from all over the world. I love seeing Mandarin, Spanish, Farsi, etc. etc. etc. being spoken alongside English here. I think it is a net positive.
I don't know. I'm rambling. I guess in answer to your last question, I would disagree.