I tend to gravitate towards darker themes in media as long as there is some level of substance to them, though even I have my standards of when something is just bit too dark for its own good.

SMT and it Persona are cases of a good darkness, as there is usually a purpose behind it and the series is about exploring the darker side of human nature and culture. Course this is all intentional as the original development team was trying to give their games a different contrast to the melodrama of Final Fantasy, Space opera of Phantasy Star, and the family friendly Dragon Quest. They went with a darker 80s punk vibe.

I'm not bothered by the themes explored by the series, and I'm happy it does exist in the medium because there are very few truly dark RPGs that don't subscribe to a more idealistic view of the world. While there is nothing wrong with idealism in gaming, I feel it is often overdone, so I am happy to have a franchise that can give me a more cynical taste of things. The fact the series appeals to my misanthropic tendencies probably helps as well. Even then, the franchise isn't without its idealistic undertones. Persona is all about the power of friendship, and SMT itself has a central theme of moderation. Again, the darker imagery and elements simply work because there is an actual theme to all of it, even if some of it is simply stylish.