I never completely understood this. I guess it's partly a kneejerk reaction to the nominally left-wing repressive regimes they left behind. Another component is probably a sudden immersion into a truly pluralistic society when coming from an intolerant and homogenous one. But still, I can't say I truly understand it.
I'm in my 30s and this is still a source of conflict between my family and me. They're lower-class "real people" who have a soft spot for despots on the Putin spectrum. Because while they're pro-democracy, they also think you need a "firm hand" to keep all "those people" in line, and by "those people" they mean people they can't or won't empathise with: poor black people, the stew of "educated degenerates" who refuse to have normal sexualities or lifestyles, muslims, and so on.
The reason they are against asylum seekers may be simpler as it seems: they know that the situation was going to create troubles and escalate, and therefore it will be blamed on the dark ones (the focus is on them). Can you distinguish a Turkish from a Syrian, for example? Furthermore, with this huge expenses for refugees, the social money is likely to be reduced, and I don't have the numbers, but many of them live off of the social security provided by the state. (without even considering the money they get for the kids)
I mean, I do understand their concerns, which is really sad...
Many dark foreigners have the same point of view. In such white countries, more dark foreigners mean more chance of troubles for them. Dark, slightly dark, black, etc, they all belong in one category: dark foreigners. Even Indians, who do not have absolutely anything in common with Africans, for example, still belong to the same category.
If an Indian does something bad, dark people will suffer from it.
Same for social security: they'll have less, considering that many (poor) foreigners will come, and they may have to share the resources.
It's all about survival...