The problem comes when the alternative scenarios are not credible.
This is not, say, like the question of whether three men managed to escape from Alcatraz in 1962. We know that it would have been very difficult, but we know it was survivable, and there seem to be enough claims of different people having seen some of these people to at least make this seem possible. There also is not any evidence, like their bodies, suggesting they necessarily died.
This is much more like the idea of whether Jimmy Hoffa, far from getting killed by the mob, had actually decided that day in Detroit to abandon everything and go off to live on a remote Pacific island. Sure, maybe it is possible that Hoffa was tired of everything--the weather, his family, the union, the politics, all of it--and that he had connections no one in his life knew about that he could use to relocate himself without anyone knowing. That is technically possible, sure, but it is also really contrived. Advancing an alternative hypothesis is one thing, but if you are going to take it as being a credible alternative it has to be somewhat credible. Arguing that this Pacific hypothesis is just as worthy of consideration as the idea he was killed by the Mafia seems like fallacious reasoning.
This is especially the case given that the sex trafficking hypothesis seems to have been created out of nothing by family members, people who have literally been found to have lied under oath in court with the goal of not introducing any claimed sightings that could contradict their story.
If anything, the Netflix documentary has given greater context to the family's claims and the reason for the claims. They were never that plausible, requiring sex traffickers to behave in hugely risky ways that did not make sense for them. Kidnapping random tourists? Letting them travel freely across borders? The documentary provides a lot of evidence that suggests this could be a weird sort of mutation with their pre-disappearance concern over how Amy was not being straight and heteronormative enough for them, a fixation that never had a chance to evolve because it was caught in amber by Amy's disappearance.
Compare how the Sodder family insisted that the missing Sodder children were alive, removed by a conspiracy at once so powerful as to abduct five children from inside a burning house yet so weak as to allow them to live and send occasional ambiguous signs they were alive. The children certainly had not been killed in a house fire triggered by faulty wiring that at least two different people warned them about, and they surely had not missed the few remains left after a long hot fire.
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