For reference: They summary executed/murdered thousands in the Philippines and it didn’t work..

El Salvador shows how it can work, of course what went down there also wouldn't fly in Europe but crucially they didn't actually go around and murdered people en masse -- they rather humiliated them and dished out long prison sentences left and right not particularly caring whether they put away innocent people.

The primary goal was to make sure that the country isn't a constant war-zone any more, to get the violence off the streets, and in that the policy succeeded. It was harsh, but not heartless -- all those humiliated and locked-up people do still have chances in life, at least in principle. Parents can hope for their kids instead of mourn them. In other areas Bukele is just as much of an idiot as other techbros. But as far as dictators go he's one of the good ones, so far, whether his long-term legacy will be "tough man who did what he had to do to save the country" or "tough man who tried to save the country and made everything even worse by getting rid of the rule of law" is up in the air. El Salvador might turn into Haiti, into Uruguay, or Singapore. Who knows.

Basically, what you want it is to make crime an irrational decision but making sure that it doesn’t pay of.

That alone isn't enough, you also need to provide alternatives or people are going to take their chance. In El Salvador the situation was so bad that the government didn't really have to do anything in that regard -- once the daily shootouts on the streets are gone people have the opportunity to sell fast food on the street, again, generally do business. But in a European setting mere cracking down won't be enough. Or, in other words: Things aren't nearly bad enough in Sweden to even begin to justify even entertaining the El Salvador solution.

The best criminal policy is social policy.