But there are solos in many other genres, and spoken word isn't even that common in metal. So these are poor arguments for calling Slipknot metal.
You missed the important part:
"Please expand on where you see this influence in their music, and how this overrides all the other non-metal influences in their music and makes them undeniably metal."
So stop dancing around and explain your position on this point.
No, the primary influence behind Slayer was metal. The punk influence complimented the metal core. If the biggest influence on Slayer was punk then they would be a punk band.
Why? How can a punk subgenre be metal? How is this different from calling thrash metal punk?
Again, this just seems like you have a fuzzy conception of what metal is all about.
Slayer didn't start using hardcore oriented riffs in abundance until the late 1990s when people started calling them nu metal, so I'm not sure how well that argument holds up.
Last I checked not much metal is either.
How can you even say they are trying to play metal? Look at the intent of their music, what they are trying to convey - how can you kid yourself for one second that this band is trying to be metal? This is the most important consideration, as art there is virtually *nothing* Slipknot has in common with metal, and musically we have clearly shown that their influence lies elsewhere.
You have failed to prove first that there is significant metal influence in Slipknot, and second that this influence is the primary element in their music. And the second point is as far as I can see impossible to prove, as the primary element, the core, the main message is not something familiar and integral to metal, but "I'm different, I'm special, I don't fit in, no one understands me, etc.". This should scream 1990s hard alternative rock (nu metal) to you, not metal.
Just pointing out that when people have written dozens of reasons why Slipknot may be metal that posting "I just think it's bizarre that ppl think they are not metal just because a bunch of 13 year olds listen to them" makes it seem like you probably aren't really keeping up with the discussion.