SMT isn't about demon worship. I'd even go as far as to say the opposite because they make it quite clear demons are not friends and are more like "allies," basically like a bodyguard that you probably shouldn't fully trust in the narrative. They'll keep you safe after negotiation, but are not your buddies in the slightest, some will even outright refuse to cooperate if you have a different alignment. Demons are also the reason why SMT games are so post apocalyptic. The games typically have an alignment system between Law, Neutral and Chaos which influence the ending, and none are really about worshipping who you side with. Really it's about what the aftermath of the world will be due to your choice, consequences and all, and what you do it. Haven't gotten to the end of Devil Survivor specifically, so I can't speak for that. Also it's never really explained until maybe like SMT V, but demons aren't really always demons. A lot of lesser gods, mythical beings, and sometimes historical figures get classed as "demons" as well, its more like a general term used because the very thing you use is called the "Demon Summoning Program." If anything, "demons" are more like beings based on the human takes on these figures that tend to all be violent and sentient. It's also worth mentioning there's a lot of SMT spinoff games that ditch the religious theme altogether, like Persona, Devil Summoner (despite the name), Tokyo Mirage Sessions, SMT if, Maken X, and so on. Devil Survivor itself is a spinoff.
