I agree that making fake evil magic books is not something we should do, for a variety of option.
But I don't think it's encouraging people to go cultist. You only get evil magic books if you look for them, generally. Mathilde wouldn't exactly go and hand them out at dinner parties or spam people with them. Also, it's not like you do a ritual by accident. Or that people don't know that magic is dangerous shit. Like, maybe we have different things in mind of what type of fake book this is about, but I wasn't thinking of something subtle that might be inoffensive at first glance. I was thinking a proper necromancy or something like that.
To make a comparison: If I make a fake dating profile on a cheating site, and then link someone to that, I arguably have some moral responsibility if they try to hook up with that fake person. I did technically tempt them. But that doesn't mean they didn't behave in a way that deserves some asskicking. They still had a choice both in following the link (acquiring the book) and then going through with it (trying to perform the ritual).
Sometimes a person doesn't get a choice (possessed by a daemon), but that's not the case for the fake dating site. There's also cases where cheating is at least kinda understandable if still shit, like if you're in a shitty marriage and your partner is already cheating so it's like things can get much worse. That would be Vanhel and his Skaven invaded lands, or the Grand Theognist in the Vampire Wars. But those cases are pretty fucking rare.
I do not think it works like that, it feels a bit like essencializing potential cultists: there are bad people who when presented with a evil book will turn cultist and then there is everyone else. The problem with that is Chaos (and to a lesser extent necromacy) is about temptation. A lot of people fall because they had just the wrong book fall into their hands at just the wrong moment, or just the wrong daemonic whisper, others do indeed go looking for the power of Chaos but not out of a generic desire to do evil but because they have some burning passion that supersedes faith and reason both, avenging a destroyed home, bringing a loved one from the dead. A false book of dark lore would catch the desperate as much as the ambitious and the mad and since it will be designed to show each their heart's desire it would catch far more people than would have otherwise Fallen.