There are such " perspectives" that it's as if they were put there with a sledgehammer, trying to leave a wet spot instead of "evil character" (of course, old "evil" characters of BG2 were the first candidates for this role) or the psyche of the player, if the player has the nerve not to support Larian's own perspectives (this is already something that concerns directly Larian "evil characters"). Clearly, someone who plays "good" is fine with it and doesn't see it that way - tastes differ, with different playthroughs, of course, there will be different experiences. The thing is, in BG2 it was "okay" for everyone to play - I don't remember a single review or opinion that the game tries to impose something, "teach" something, or favors "good" characters over "evil" ones, or tries to "punish" the player with "isolation" or worse for them "going the wrong way". So what Larian did with Viconia and Sarevok is perfectly invested in their concept and shows their " perspective". That's how you should "show evil." So that no one likes it. Those who haven't played BG2 will believe it ("Oh, your favorite companion was Viconia? That creepy aunt? She probably wasn't any better when she was younger, come on..."), those who have played are predictably outraged by it. Honestly, in my playthrough I wasn't surprised by it and took it as a given simply because by that time I had already spoilered Astarion's "redemptive ending", "liked to degrade myself", read all sorts of articles, talked to an acquaintance who was playing purely "evil", I came to the temple of Shar quite late, and saw Sarevok near the end of the game as the last quest before the final battle. The only difference with the OP in this thread is that it didn't surprise me, it wasn't a surprise, just an extra brick in the main building. Well, or a brick on the head, depending on how much someone who played BG2 appreciated these characters.
Jaheira tells Karlach in this scene that Karlach "really deserved it" (referring to the ritual, not verbatim, can't find a nearby save). The whole thing seems like an unfinished opportunity, no, there was no specific explanation there that it can only and exclusively be done by druids, just a line about it being a druidic ritual. Then Jaheira starts spouting all sorts of philosophy, Karlach gets all excited about it (and the fact that she's probably going to die soon, probably too). There's no coherent explanation about the ritual not working and why, or about how it can't be applied to anyone but Jaheira, so it's unclear whether this is unfinished content, or whether after "blah blah blah immortality fu" the player has to be convinced, realize that "fu" and appreciate the "philosophical implication".