Why would you be insane for reading it? If you read it all and believed that was exactly the way to treat witches, and then went around throwing us into ponds or torturing captives with medieval implements, then maybe that would be insane, not to mention illegal and rude.
But just reading it grants information and insight into the era of witch hunts. I think it's good to know history so that we can learn from it, and be able to see how it affected the present.
What you read doesn't make you insane. It depends on why you picked it up, why you continue reading, and what you do with that knowledge after. I skimmed excerpts of this book, and maybe one day I'll sit down to read it all the way through. I just haven't been in the right mindset to get engrossed with it, but that certainly doesn't mean that I'm sane. So don't worry about it!