If Merlin wrote them, then I see it as Einstein writing about nuclear physics. It was already there, he just documented it.
The Blackstaff isn't really an exception. It is an item that takes the taint instead of the user. The orignal owner of it still wants it back too, according to Jim.
How is Necromancy and the summoning of beings anti-thetical to life not evil? Those are some of the worst. Time travel manitains the status quo, sure, but that is because a paradox may destroy reality. They don't want to risk it happening, that is for sure. How has Rashid broken the 6th Law? As for the Seventh, he doesn't have to summon them in order to keep them locked up. He just needs to check the locks, throw a couple bars over the door, and banish the few that get in.
That's what breaking a Law does. It corrupts you. It is a stain anyone (with power) can see, and it changes you.
I doubt a wizard of any caliber could do that last bit. And who is immune to them, beside the Blackstaff (who has his filtering tool)?
In the book, it isn't phrased like he discovered them, its phrased like he created them. But then again its only a sentence that mentions it. Without more information we can't really know.
The Blackstaff is an exception because it has the ability to take 'taint' into it. The fact that this ability even exists means that its within the bounds of reality to resist the 'taint' of the Law of Magic, through magical means (assuming the Blackstaff was enchanted to resist the 'taint').
Well, calling back/using souls is evil, but I wouldn't say that the use of dead corpses which don't have a mind/soul within them is evil, but this is more of a philosophical issue. (I would see the other laws of Magic used to protect a being with choice, ie a mortal - I wouldn't consider a body with a vacated spirit a mortal anymore, hence its not evil to use it). As for the risk of breaking reality, any magic has inherient risks with it. The difference between the first four laws and the sixth and seventh laws are that the first four prohibit actions which will
always lead to a mortal's choice being stolen (ie evil), whereas the sixth and seventh prohibit actions which
might if used inappropriately lead to a mortal's choice being stolen, just with much larger consequences. In this sense, I see the sixth and seventh laws as 'evil' as using any other type of magic - they have the capacity for evil, but don't directly lead to it.
Its not directly stated in the books, but in both Turn Coat, for instance, and the RPG books, it says that Harry suspects the Gatekeeper has broken the 6th law, although we don't really see it. And the 7th law isn't just collaborating with Outsiders, its trying to learn any knowledge at all about them. And this is the Gatekeeper's job. So he is in a constant state of violating the 7th law, and Harry suspects that he violates the 6th law, and Harry has pretty good instincts.
Overall though, there are too many questions to say definitively that "The laws of magic are absolute" or "The laws of magic are fabricated", so there's no use arguing over it. I guess we'll find out in future books, but in the meantime, there is plenty of leeway to go one way or the other inside a campaign.