People really love quick-fix bandaids with immediate results, no matter what the long-term consequences , then call the problem "solved" even though the root causes haven't even been addressed and long-term consequences aren't even known.
Some obvious caveats to the "feel-good" story.
* Murders in El Salvador have been on a strong downward trend since 2016, three years before this leader took power and six years before these draconian measures were implemented.
* Considering that many shooters are responsible for multiple bodies, and a lot of killers get got themselves, there were likely only a few hundred murderers operating in El Salvador. Which suggests that 99% of the 40,000 people rounded up weren't killers at all. A large number of them had likely been responsible for other crimes. Others were only involved in gangs at all because they were forced at threat of their own life or that of their family members. Others had likely left the life entirely. We have literally no way of knowing what crimes they've committed or who might be innocent, because the round-up isn't even requiring any evidence of specific crimes, just a mere accusation of affiliation.
* In the year directly after the roundup, a few hundred fewer murders were committed. But just as many murders as that were still committed, which casts some doubt on the framing of the initiative as some sort of total wipeout of violent gang activity. Those few hundred fewer murders are the probable one-year impact, but what are the consequences going forward? Did this "solve" the problem, or did it simply slightly accelerate the already existing trend? Will these 40,000 uncharged inmates without rights be imprisoned for 5 years, 10 years, 40 years? If their incarceration is short-term, will they be less violent or more violent when they get out? Will their children be more likely or less likely to grow up dysfunctional themselves, especially the children of those who weren't in the game, had already left, or were going to soon? If the incarceration is long-term, how will the nation afford it, especially considering the likely need to continue incarcerating tens of thousands more as murders have and will continue?
* What is the eventual out for those who did not do anything to deserve indefinite imprisonment? Will any sort of reasonable human rights for a defense be granted at some point? How many of those are there....1000? 5000? 10,000? What's the equation to decide how many X lives can be ruined to save Y others....especially considering that many of the potential victims were likely other now incarcerated persons?
Before dismissing these questions, remember that all of the exact same rationales which defend these practices are also used in the USA. Most obviously, to defend police shootings, because some 1000 a year killed by the police supposedly keeps innocent civilians or officers from being killed, and if some of them were not actually trying to take anyone's life, well too bad - they were in the wrong place at the wrong time and likely bad people anyway. Sometimes you have to kill a few innocents to maintain that thin blue line, right?