They think that if they tell that lie enough, that everyone will believe it.
I live in Spain and know a lot of Swedes who come here to escape the winter cold. Muslims are a problem but mostly to themselves. If you want an analogy consider when there was a wave of Italian immigration to America. It brought the Mafia and the violence that came with it but as a result of it few people would have said America wasn’t a good place to live. Maybe that is why Sweden still makes the list of top places in the world to live.