I appreciate your comments and I'm sure you know a lot more about underlying security mechanisms than I do. That said, the proof is in the pudding - I've never seen a Mac hijacked by malware, and almost every PC I've seen at some point or another has been.
The market share argument is total bullocks. For a security expert you seem somewhat ignorant of the "not-a-zero-sum-game" principle, by which there is (throughout broader society) no demonstrated correlation between the preponderance (market share) of targets and the quantity of attempts to attack them. Hence, despite the fact that the wealthy only represent a small fraction of human society (I dunno, like 5%? Smaller than Apple's computer share, to be sure), they are still targeted *more* often by thieves than the huddled masses, etc: Why? Because even though there are far more average people (with or without in-home-security) to attack, the wealthy present a compelling opportunity. Why only try to steal from one when you could steal from both? You can apply this argument almost anything; go wild. Remember also that malware has been written and circulated for nuclear plant controller system software (I forget the details, but I think the total install base for this particular package is like 5 or 6 units - but still represented a "compelling opportunity" for someone).
Further, by virtue of the fact that Mac's aren't loaded with 3rd party security software, that their users don't expect malware, that there is NOTHING else in Mac malware space, and that the demographic of Mac users is financially "elite" - if I were a hacker, I can tell you which niche platform I'd have my eye on. It's pretty obvious. Not worth the effort? Really? Says you.