I'm king of reaching the limit of my knowledge here. But I'll try to give it a go. I am quoting CuriousQuercus' last post:
Demons of the western religion are fallen angels, but what about other religions that have demons?
I believe there is fallacy in considering that the demons in one culture are demons in another. As you say, what about other religions?
I will note here that demons are not just part of religions. If they exist, then they exist. They may be part of a certain culture and only deal with people with that heritage or who live in that area. I doubt I will find a djinn hanging out around in suburban California, but if I moved to Iran I might be able to meet one. It doesn't matter if I convert to Islam or not, they will still be there (whether they pay attention to me or not is another matter). If all religions suddenly ceased to exist, all these spirits would still be where they are and most of them would still be performing the same function.
Christianity seems to be an extremist religion when it comes to good/evil. When you only have God and Satan, the sides are going to be pretty damned polarized, you know?
So I was reading a -very- brief introductory article about common Hindu themes, including gods and demons and the article describes their relationship as necessary, complementary forces. Not that this justifies Mengele, may he rot for an eternity, but the idea of demons being well, necessary to maintain balance, an idea that would be rejected pretty quickly in most churches.
I feel like you are thinking from a very Judeo-Christian-centric point of view. Why does it matter what most churches think? Most churches are wrong. The business of most Christians is to reject everything that goes against God, not to understand it. There are many religions and spiritualities which deal with the Dark from a perspective of respect and necessity. Those are probably the ones to ask about the nature of demons and dark entities. Christians don't want balance, they want evil to be destroyed and have their god of ultimate goodness rule the earth. Iirc, even hell itself will be destroyed at the end. So to them, this is not an issue of balance. This is an issue of destroying everything against the nature of their god. That is probably not a good perspective to take while trying to learn about demons in an intellectual way.
This text however was written by someone to be used more like a set of instructions to "bind" or force any of the 72 demons listed into a circle to at least listen to you for a period of time if they refuse to help. Something tells me if anyone tried to someone a demon and if anyone answered, they were not too thrilled about being temporarily trapped and were probably not too cooperative. The author is supposed to be anonymous for good reason, the author would have been (and may still have been) killed for it.
Just passing the buck here, but it is fairly well known that grimoires of these type were originally published with errors in the text that would make the instructions either useless or highly dangerous.
That being said, I imagine there are other ways to summon a demon. There are rules to the universe, right. Ceremonial magic is all about those rules - the physical actions you can take that will reverberate through other worlds (or at least, that is how I understand it). I believe even people with no power of their own can find a proper set of instructions and summon a demon. But if you do have power of your own, you can go about it in other ways.
Have you read The Marriage of Heaven and Hell by William Blake? He was an interesting guy; he often spoke with Christian spirits. This read is short, you could probably get through it in half an hour or so.
Here is a quote I quite enjoy from that work:
"If the doors of perception were cleansed every thing would appear to man as it is, infinite.
For man has closed himself up, till he sees all things thro' narow chinks of his cavern."