Completely understandable, and I respect your opinion. This is mine.
I feel there are many more ways spells could be used successfully then simply "they must become the bad guys". I recommend my own video on understanding mythos magic here, and this will form the basis of my entire argument, but spells are useful most as a Plot Device. When they are taken as more than stats on a sheet of paper and instead serve the unfolding narrative, that is when they are most useful. And yes, experienced Keepers very much know how to improvise and adapt as the game sees fit. For example, I never tell the players exactly how a spell works. Ever. That way, it can work as I need it to and will never break the game because spells can work differently in different situations. Spells do NOT have to be a game changer or something that takes away from the atmosphere. Anything can be used to increase the horror aspect and move the story forward, including "magic".
And yes, I appreciate you taking the time to write all this and again want this to be my argument back, not in any way I'm right and you're wrong.
I would disagree with the generalization that all investigators are automatically good and all cultists and monsters are automatically bad. Slightly more true would be all investigators are ignorant whilst all Mythos entities are enlightened, but this too is a generalization (The Idiot God Athathoth for example of stupid enemies, although the point could be made that the Crawling Chaos is technically an extension of aforementioned god and acts as his intelligence...). No Call of Cthulhu is not a fantasy RPG, it is horror. And horror has some themes of curses, spells, and the summoning of daemons which permeate the genre. While the "bad guys" use are often the main magic users, the good guys sometimes need to use a spell or two to attempt to defeat the darkness. Then again, the plot device that all magic should serve as comes into play, and there are many different ways a keeper can utilize the uncanny and unholy nature of magic and spells against the players, even as the players try to bend the magiks to their personal will.
One thing I always say about CoC magic (again, check my video on Mythos Magic:) is that it must come at a cost. It seems your major argument against magic is that it ruins the mood of the horror game, but that means you don't understand the way magic in CoC is supposed to work, at least in my opinion. Anytime the Investigators attempt to use or understand the eldritch, there should be a cost. And this actually will strengthen the players sense they that are nothing but inferior or an ordinary person (not even hero in most cases, to me Call of Cthulhu has the players as victims, whereas D&D and RQ and similar fantasy systems uses the "hero" stereotype. Magic in Call of Cthulhu also greatly differs from that of D&D because of both the cost in sanity / magic points (which keepers should portray more than just saying you lose 10 sanity, they should make the role-play embedded into the losses and gains of the Investigator, imo), and the way the spells actually work. There are very few utility spells in CoC, and even the "utility spells" come with costs not to be taken lightly, plus homebrewing even more complex spells always helps. And again I stress the point of not ever letting your players know exactly what a spell will do.
The way spells in CoC are supposed to work and be used, I don't think there will ever be danger of a player confusing this game with D&D 5E.
Very true, magic is rare. No one on here ever said there had to be magic or spellcasting every session, so I mean, we basically know this already.
As to your point that magic is shunned by society, I completely agree and feel you can play this up tremendously in any game you run. But no, not all people who cast spells are automatically enemies of that which is good. Often they are just ignorant.
This is interesting, but it's a home rule and not in any way necessary unless you are letting your players abuse the magic system. If a player wants to be an occultist let them, the keeper should be able to work with that and make the story still terrifying. The magic is unpredictable and takes more from the caster than it ever gives them. I personally houserule most anything that needs it, and will reiterate to you what I say constantly to everyone. If the "point about Call of Cthulhu" is the creation of a collaborative horror story, then the rules are just suggestions! If you decide it would work better for the story for a player to be able to cast a spell the moment they read it from the scrap of paper, then feel free. If you decide it would work far better if the player had to study the spells for years before being able to cast it, that works just as well. It all depends on the scenario and the situation, and the main thing every keeper must learn is not to be constrained by the rules.
I think you should start using magic so it always works for you, rather than sticking to the rulebook or spell description, but that is just my opinion.
This does not help your point, since this is a horror game. If a member of the group suddenly begins a downward spiral into madness that began with a spellcasting, it works perfectly into everything Call of Cthulhu represents.
The players feeling comfortable is almost never the main idea of the game. Simply do not give your players spells they can abuse, and I say again, just don't give them the statistics for the spell and use the spell to the story's advantage at all times. Push the horror. If you use the spells included with the Keepers guide, there will never be any way a person can become anything like a mage in d&d, because the magic is fundamentally evil and working against the player (in most cases, this is also a generalization, but to me a necessary one).
True, but this game is definitely not balanced, and the point is actually not fighting or defeating the big bad (in my experience). I have never heard this argument before, but let's assume it does exist and is prevalent.
Investigators do not need spells, and spells will often not help them even if they had them. If the players are just saying "what dice do I roll", it's your job as the keeper to push them off the cliff. Narrate and get them into it, show them how anything that happens to the character sheet should be role-played. Also, and I say this because I know people who do it, do not be condescending or tell them they are doing something wrong. Instead, show them how much better role-playing in the RPG is:)
Thank you for taking the time both to write all this and to read my opinion on it. I believe anyone who thinks magic in CoC works like this is misunderstanding the intention of the magic system. And furthermore, anyone who allows the rules and system to get in the way of their games need to reassess their priorities. When you use spells, don't let them EVER be like the D&D spells. Name them unpronounceable names, give them crazy components and weird problems to be solved, use moral dilemmas to up the horror, implement the stages of fear, never let you players know exactly what's going to happen, and always push the horror.