I have yet to see a convincing or credible argument proving it.
Exactly. A challenge. You have Apple and a load of Apple and Linux fanboys running around screaming that their respective operating systems are invincible. You have Google running ONLY Linux or OS X (Google now longer allow their employees to use Windows because of security issues). You have corporations and governments all over the world running only Unix or Linux on their servers (as I said, Windows Server is not scalable nor does it run on anything other than BS Intel chips, no high end SPARC chips which drill Intels offering into the ground if the software can be coded to take advantage of all the threads they offer). Anyway, I'm going off topic, basically, who would not want to be the first person to successfully develop and deploy a Unix virus?
True, nothing is invincible.
I refer you to this post and my previous post.
I refer you to my previous post again. Windows has 70,000 viruses because of complete and utter incompetence on design. They can't even claim ignorance, because Unix has had features like the user and software not running in admin mode forever. That's not ignorance, that's pure incompetence. Microsoft then drags all this legacy code throughout modern versions of Windows to ensure backwards compatibility. Apple packaged their Mac OS 9 classic environment (Mac OS 9 having hundreds of viruses and half the marketshare of OS X I should add!) into an emulator, which they then scrapped in 2006. So when some security hole that's been present in Windows for 15 years (and I can name several) still exists in Windows 8, you'll know why. Because if they fixed it, it would break something important. Can I say the word again? Incompetence. I like that word. Still, can't blame them forever, they took their whipping with Vista.
Software, ease of use (excluding OS X), and support. If you're Dell breaks, Dell will drive to your office and fix it that day, on site. If your Mac breaks, you send it off in a box, or take it to an Apple store, and get it back some days later. Whilst that's fine for a consumer, that is not acceptable to a company. And as I mentioned, nothing but Unix or Linux runs on any large scale servers. Take a trip down to Apple's new server farm, or Google's many server farms. Find out if they're running Unix or Server 2008 (I'm loling at the thought). Even Microsoft runs Linux. Windows Server 2008 is simply not suitable.