In fairness to Klarna, the interest rates they charge are typically low or even zero. The problem is more that they're encouraging poor people to waste money on things they probably shouldn't buy in the first place, like expensive concert tickets or consumer electronics.
I used to work at a competitor to klarna so take this with a grain of salt, but the zero interest rates aren't really zero. They finance either by klarna eating into their runway, or by the business paying the interest up front. Which usually leads to higher prices for everyone, regardless of you using klarna or not