Absolutely. If the stories were meant to turn out happily, they would have. Undoing a tragic ending isn't "fixing" the story, it's breaking it.
A point of clarification: my discussion of "fixing" the ending of Charlie X (which I described as inhumane) was in the context of a thought experiment I posed earlier in that post about which episodes could be "fixed" by a follow-up that gives depth to the original episode (by further exploring or expanding upon an idea/theme/personal angle that was latent or underdeveloped in original episode) but, importantly, *without* retconning the episode. That latter limitation is, to me, what is interesting about the thought experiment. So just for the record, I am not suggesting that anyone write a follow-up to Charlie X that changes what happens in the episode, even the ending. Nor, for that matter, am I suggesting that someone write a follow up that tacks on a happy ending that simply negates what we see in the episode. I wouldn't buy that book and might well throw my shoe into the machine that is printing it.
I do, however, believe that the episode is in need of "fixing" in the sense in which I am using the term-- further developing a theme that is underdeveloped in the episode to give a depth to the episode that at present is nearly but not quite there. Here's what happens in this episode, from my perspective: an incredibly vulnerable adolescent (who is emotionally and socially far younger) forces his way onto our heroes' ship. Despite a life story that (to a modern viewer) cries out for massive intervention and a very gradual, guided acclimation to human life, he is immediately thrown into the mix on the enterprise, left to wander around on his own and figure things (and people) out for himself. Amongst the Academy-educated crew of the best ship in fleet (so by definition the best of the best) he quickly appears as awkward, socially inept, a loser. But in responding to his awkward behavior, he is judged by the standards of this society of winners, and even his unhealthy fixation on Rand (the first woman he has *ever* seen) is written off as his "first love," much as the rest of them had once had.
Spock, despite being an outsider himself, comes across as callous (and clueless) in his limited dealings with him. McCoy, who (I believe) elsewhere in the series is described as having a psychology specialty, demonstrates very little understanding of what Charlie might be going through (or interest in considering the enigma of his emotional and intellectual development alone from age 3, which even to most lay people would seem to be a behavioral question worth exploring). Despite knowing he is being viewed as a father figure Kirk has no time for him, and (tellingly) his only attempt to bond or provide guidance to Charlie is to teach him some fighting techniques-- to 'man up,' as it were. (There is metaphorical heft to the fact that Charlie, who desperately needs a hug, getting thrown across the floor in his only physical contact with Kirk). Indeed, Kirk only pays any real attention to him when the task falls to Kirk to get Charlie to stop pursuing Rand, at which point Kirk gets to move into the tough-guy mode with which he is more comfortable, getting up in Charlie's face as though he is reprimanding one of his Academy-educated subordinates who should know better. But there is no acknowledgment that of course Charlie doesn't know better, and could not reasonably be expected to know better. Uhura uses him (and his apparently inherently comical fascination with Rand) as a punchline in an improvised cabaret piece.
Charlie becomes a threat, and starts killing and maiming people. In the end, the Thasians appear and say they must take him back as he is a threat. Kirk says he should be with his own people. The Thasians say that that is impossible, as he will always be a threat. They do not explain why he could not be stripped of his powers, or somehow controlled, but the bridge crew seem satisfied with the explanation that will get him off their ship. They do not discuss any compromise arrangements by which Charlie could be visited by humans while in Thasians' care, and there is no questions asked of under what conditions Charlie will be kept by the Thasians. Charlie begs to stay, explaining that the Thasians have no love and he can't touch them, but the crew lets him be taken away. Although Uhura and Rand emote as Charlie is taken, the male members of the crew (including his father figure) show no emotions (Spock forgiven on this point, I suppose) and do not even say goodbye. Once he's gone, Kirk assures Rand that it's all over (for them).
Not all science fiction is allegory, but to me it's hard not to see Charlie as a "troubled" teenager, reeling from trauma and clumsily seeking love and acceptance, who is ignored until he becomes a (legitimate) threat to others, at which point is he is incarcerated, and everyone else moves with their lives without questioning their own behavior. To leave the story there-- with none of our heroes considering their own culpability and no exploration of what then happens to Charlie-- strikes me as inhumane storytelling. Certainly it is missing the compassion that marks Star Trek at its best.
So a follow-up that could "fix" this story would explore that culpability and those consequences-- a time when our heroes got it so wrong, perhaps because they are heroes and don't (or won't) understand those who are not. And what makes it so tempting is that (as shown above) this message is almost there, in the episode-- the episode *almost* criticizes our heroes (in the way that "Is There in Truth No Beauty?" does manage to criticize them, to some extent at least) for the way that their otherwise 'heroic' behavior and character traits impact a vulnerable non-hero. That's where I see the possibility of a "fix" through a follow-up. Without that, the episode is just very well crafted monster-of-the-week stuff.
