Some points to some people.
"I've never seen anyone install a Unix-like OS on a Mac."
Most famously, Linus-yes-that-guy did. As already mentioned, back then the mac mini made sense as a nice small form factor computing box.
As for the price premium, well, "windows tax". IME macos x is better value even if you end up not using it. If you plan to sell the hardware on later, then macintosh is your best bet for retaining value, too.
"The justification for using Macs is that they are "more secure than windows" (don't get me started) but they haven't even installed AV, one good Mac virus and we're screwed."
Well, windows has a couple problems, mostly the complete absence of security fences inside the system, that macosx plain doesn't have. This largely removes the point of making macos viruses and other malware in the first place. Thus, even though there is a considerable installed base that makes sense to target, you don't see rampant mac malware that often. Just like you don't see rampant linux malware very often.
I strongly disagree with the implication that absence of third-party anti-virus is a bad sign: It means you've bought into the notion that buying a system unfit for putting on the public internet before installing at least one third-party security patch up "solution" is perfectly valid. To me, it signifies inferior software.
Why yes, I am perfectly fine with running my system of choice an "unpatched" recent release, default install, without so much of a firewall (packet filter, really) active, right on the public internet. I'd even be fine with running a variety of open source (so everybody can exactly see where the weaknesses are) software on it to serve up various services. Done it for years, in fact.
Of course, that's server installs with all sorts of unneeded things thoroughly disabled, deinstalled, or never installed in the first place. And I only do that after double-checking that my idea of what is running matches reality, that I understand the risks and that it's setup such that the worst effects of possible breaches, should they happen anyway, are sufficiently mitigated. But yes, I have no trouble with that. Software fit for purpose doesn't need third-party add-ons to fulfill its purpose.
"[macos x] differs in subtle and irritating ways from the RedHat and Debian based distros I'm used to."
That would be because the redhat and debian default installs --which you're not required to use and each can be made to behave entirely differently-- are tuned to be more or less "windows like". You could try and tune them to be more "mac like". And you can.
Apple doesn't really let you change your desktop environment to be something completely different than what they intended. gnome and kde are plenty more flexible there but best of all, you don't have to use them and could kick them out and use something else entirely, and still run all the programs that don't have a kde or gnome dependency. windows claims it can do "skins" but I've never seen anyone use it. I only use it to turn off all the fancy cpu burning "features" in order to have to wait a bit less on the rum thing. It's supposed to wait on me, not the other way around, fsck it.
It would be ironic to see your gripe about macos x being less well polished than fedora or ubuntu as apple are the kings of polishing, until one realises that your gripe is more about what you're used to than about the quality of the software.
In looking around at events with lots and lots of geeks and plenty of them professionally so, looking at what they connect to the network, a large chunk up to about half are apple laptops. Of the rest, walking around it's easy to see that a lot of them are thinkpads but they don't stand out by mac address.
This isn't to say that your choices are invalid, just that they're personal choices. And that's fine, as long as you recognise that they are individual preferences and not hard fact. How this meshes with company policy and "enterprise" locked down desktops is a different discussion. Me, I'd have to adjust to windows, macos x, and all default linux distribution installs, simply because I use and am used to something so wildly different*.
* If you must know, wmx/wm2 on X, lots of xterms, some browser windows (firefox, moving to opera), heavy use of screen and (n)vi. No desktop environment to speak of. Not linux, no. Though as I recently found out, for me the quickest way to take the most irritating edge off a default ubuntu is "xset r rate 250 50".