Riyadh would make a much better target.
No, the radical islamist don't care who dies, but they're known by families, and financial backers, and many others who do care. Others who care enough to turn them in and change the direction of the talks. MAD is the only answer. It's worked before and it can work again. And it can't just be Mecca. If they nuke us, we nuke them. No holds barred.