Unfortunately, they're huge, and I doubt the Swedish authorities will do more than give them a fine and a slap on the wrist.
So what? It's 0% interest. It's incredibly helpful to have easy-access financing to split purchases across a few months.
>even simple things like buying a book through a web site requires declining several offers for paying with credit.
This sounds so specific it seems like you're taking a bad experience with one website and pretending all websites are like this. Most e-commerce sites I've used in the past year offer Klarna or some similar service and all of them have been implemented as just another option in a set of radio buttons.
Unfortunately, this often isn't the case of people who are worse off, not good at managing their finances, and often overwhelmed by bureaucracy.
They fall behind on payments, and then get taken to the cleaners on fees, deferred interest etc., often paying several times the actual price of the product. I've seen this happen (with different but similar services).
Less savvy people being sold stuff they can't afford on credit has been such a problem that some countries have made it illegal to extend credit to someone who can't afford it, which is obviously extremely hard to enforce.
This is hard to grasp for many here, because HN readers tend to be well above average intelligence. Try to think in terms of "imagine how dumb the average person is, and now realize half the people are dumber than that". Now add mental or physical health issues into the game.