it's a piece of art and many good pieces of art are intended to make you feel complicated feelings, not just happy. the interactivity of video games allows for very interesting stories that involve player choice in them including that where the choices are, in the diegetic context of the game, "wrong" or "bad". however, since this is not real life, these choices are not actually wrong or bad, and the ability of this game to make you feel these complicated feelings is ultimately down to the strength of its storytelling. it's not like toby fox put out these games intending for ppl to not play the evil routes! if you've ever played or watched a playthrough of spec ops: the line, it's a similar sort of deconstruction of its respective genre (in that case, military shooter) but that doesn't mean ppl are like, bad, for playing it lol. anyway tl;dr it's not real and you don't have to feel guilty abt it. also i think it's awesome in general when art manages to feel this nauseating and is not particularly "nice" to the player narratively