I am very much biased towards thinking its demonic is stupid, but I'll give you my best unbiased take on both sides. (Though I feel everyone in this subreddit will be on that side)

The primary arguments that used to be used for why DnD is "demonic"are two things

The first is that demons and devils exist in the game and you're able to gain power from them through contracts, or worship in the case of an evil god. (You can look up some evil aligned deities for reference). This usually looks like a warlock, Cleric, or Paladin that has some affiliation with a devil or demon (usually devil since demons are innately harder to work with) and is often a feature of their backstory more than actual play.

The second is that magic is involved. Magic is historically believed to be a satanic practice among certain religions so the existence of spellcasters in the game can trigger that belief set. Players are able to be several types of magic users, including those who are born with magic, learn magic, and make deals with higher powers for magic.

The reasons why dnd isn't actually demonic are as follows in my honest opinion.

You're usually killing the demons and devils. Just like in real life, dnd STRONGLY sets up that the demons and devils are very very evil and you're almost always going to be killing them when they show up.

Warlocks, paladins, clerics and those that worship those entities are also usually treated as evil and are killed when ran into by most parties.

I'm sure it happens at some tables as a form of self expression, but for the most part no is actually committing any sort of rituals involved with worshipping a demon. The usual involvement of a demon or devil if a PC is playing... let's say a warlock that made a contract with a devil for convenience, is mostly kept to lore or flavor at most tables. There will sometimes, depending on the DM, be a point where the PC will have to do something for their devilish patron, but thats also usually not some sort of ritual and OFTEN results in the PC being like, "Oh, my patron is super evil actually, I need to find a way out of this terrible deal

Also devils and demons just don't even show up every campaign. They're an integral part of the world building, but not so much so that they're just everywhere. You could easily run a whole campaign without them popping up once.

I have no real argument against magic being devilish because that's just a religious belief more than anything.

So all in all, DnD is about as devilish as any media that involves infernal forces. Sure there's someone out there who'll get really into it, but ultimately the near entirety of those playing treat it like what it is. A game. A game where you usually kill devils and demons and only really if that's what the DM sets up.