Right. Until now. That wasn't always the way it had to be, or always the way it could have been. You can't really argue that Star Trek couldn't handle an explicitly adult subject when we have just seen it do exactly that. No, that's what "The Raven" was about. "Retrospect" was a very thinly veiled rape allegory. There's allegory and then there's theme. Star Trek has even done allegory episodes for PTSD ("Schisms" anyone?) but since PTSD is an actual real thing, skirting around the subject matter doesn't accomplish much; the allegory winds up failing to address its own subject matter. "Let that be your last battlefield" is notable because the subject matter isn't burried in the sub-text at all. Bele's problem is that he's a RACIST. The fact that the two aliens look exactly alike to most other people is the shift that shows off racism as the absurdity that it is, and even his dialog in the episode is a very explicit stab at the Southern Democrat voting bloc ("I once heard that on some of your planets people believe they are descended from... apes.") It fails pretty spectacularly, considering Seven never actually has to deal with the consequences of her false memories and neither does the doctor. Korvan loses his career and ultimately even his life over this, and Voyager issues a collective "Oops!" and sails off into the sunset. I don't know what you consider the core tenets of science fiction to be, but the best stories don't just frame speculative problems, they also explore the consequences of the problem. This, however, is a common thread for most of the TNG era spinoffs: since the problem itself is actually fictional, there's no need to take the consequences seriously ("Force of Nature" anyone?) so once the episode ends we can just forget about it and move on.