The reason why Israel took in the Russians is because of the way the law of return was written. it is basically written after the Nuremberg Laws which defined a jew as anyone with a jewish grandparent. The communists also defined people as jewish and put a J in their passports if they had a jewish grandparent even though the person wasnt halachically jewish.
Unfortuantly the non-jewish world calls someone with a jewish father ,jewish and will persecute or kill them for it. Those people get the worst of both world, they are treated like a jew, but not really a jew