Where do you get your view that different races are better suited for different tasks (seen in a comment), and how do you get to the implied conclusion that mixed races would lose these "specializations", inherit only the bad, or that the lesser race in some way "dilutes" the better. Has any modern study ever come to the conclusion that racial or cultural mixing is for the worse in the long run?

A "mixed race" person does not mourn the loss of some imagined ancestral "purity". You can always count on a person being proud of themselves and their heritage regardless of previous mixing. The only people worrying about such purities are the ones being replaced, and that goes for both native and immigrant, because they are both being replaced by a mix. You need not worry about the vanishing of your race. You will not change, and people won't care about your race when you are not around anymore. Theirs will be what matters to them.

As a Chilean (now living in Sweden) I am a mix of europeans and natives both of whom fought to maintain the purity of their race. I'm sure both felt superior to the other. Today both of these groups are a minority in the region, and a new sense of "purity" has emerged. Needlessly if you ask me, as every "pure race" you can think of is a product of the same process. Meanwhile, I could not care less about the racial worries my ancestors had, what racial features might have disappeared or saddned by esthetical qualities that were lost. I don't think anyone cares.

I am currently taking my masters degree in theoretical physics in Sweden... is my genetic heritage allowing me to do so? If so which? The native or the european? The european is a mix of spanish and arabic, none of whom is good in racist standards. A racist viewpoint simply holds no merit.

Changing over to culture, instead of race, I would argue that time changes cultures as much as influx of foreign people, or more. You would barely recognize the culture of your own people going back 100 years; drunken, mysoginistic, violent, homophobic, religious... people with your genes who would surely stand out in the type of crime statistics you bring up. They would have basically all the qualities you're trying to pin to races coming to your country today. Either you agree that the immigrant problem is cultural, or that your race is as wicked as theirs. In fact, since the large influx of immigrants that has been going on in the last 50-80 years, Sweden has become more tolerant, equal, liberal, far less violent, and prosperous. Is it because of this influx or despite of it? Or do the traits you ascribe to race simply arise from the whims of time and circumstance?

With the rise of fast travel and internet, time will make sure your culture changes regardless of how you manage your borders.

You need not worry about the vanishing of your culture, because it will anyway. The culture that replaces yours will depend on the whims of time and circumstance and not on the constituent races present there.