It is a bit surprising for me that some Swedes (note that I wrote Swedes with a capital letter) believe they can know for sure what some Russians can or can not think or do. You are dealing with a large nation comprised of individuals, some of which like slang, some do not, but the most important thing is that you support the idea that slang should not only be included in language apprehension, but be put on the same level with the normal language, if not higher.
The type of slang that I mentioned above is criminal or criminal-inspired slang, which originated historically in specific areas of Russia and other countries and is not representative of the Russian language. Those criminals came from God knows where (as they group together by trade rather than language or culture) and they contributed a lot to the disgusting lingo of the modern criminal world. If you want to know my opinion, I do not think this language has any connection to the Russian language. It is rather part of the world history of crime. It is a disease easily picked by some uneducated youngsters and, unfortunately, some older Swedes (just kidding). Anyway, this is just my opinion, and I will not go for a war for it. Wars usually start over even less important pretexts, and there are and have been enough wars already, even if we are speaking about Internet holy wars. But I will support any constructive discussion which requires some intellect and good humour.
Getting back to the 'slang' in general, you know Russian is a very conservative language in that respect. If it was not such, it would have lost its case system and other complex aspects long ago. Of course it always had regional dialects and professional lingos e.g. sea terms, etc. But it is very hard to create a slang out of nothing, you need an occupation which this slang will be centered around. And if this occupation is robbery, drug dealing, etc. then I am not interested in such slang be it Russian, Swedish, or Cardassian.