I was using a Windows machine at home when I built the bulk of my website. :) For a time it was served off a home Linux server until the traffic got to be too much for my local ISP. I am personally platform agnostic - I can (and do) use all operating systems - each to their strength. I'll try to cover your points here:
1) Saying there is no market-share for malware and games on the Mac actually just proves my points that this makes the Mac a "better" choice in an educational environment.
2) People are frightened by the Unix prompt because they aren't educated in how to use it. This is an educational setting, so I think that isn't going to be much of a problem. It's a learning opportunity.
3) Applications and the OS can be "destroyed" by the user doing something stupid - like dragging things to the trash that they shouldn't. The people I work with are brilliant and creative and not very computer-savy. You name it, they've done it to their machines. Doesn't take a lot of work to put them right back to working again.
4) Unstable hardware - this has not been my experience in a long career of working with Macs. Yes, you get the occasional "lemon" machine that always seems to be going wrong, but you're going to get that with ANY hardware vendor. I've seen more catastrophic hardware failures in our windows boxes than I've seen in our Macs, even though they are in the distinct minority in our shop. And I'm talking name brand stuff like IBM server hardware.
5) Our shop has 3 X-Serves: Knock on wood - they NEVER go down. The first one we got was a dual G4 model - and it is still going strong to this day. That little machine was a production webserver handling some high traffic websites in it's day. These days it just does some filesharing and minor web duties.
6) Everyone says that I'm kidding myself about Mac viruses and malware - yet they never provide any examples or anecdotal evidence. My personal experience herding a group of unschooled computer users who have essentially unfettered and free access to the internet shows otherwise. The worst things these people do to their machines are:
a) downloading crap "free" fonts from the internet. Bad font management can account for more than half of all Mac OS problems. The latest version of Mac OS X comes with so many high quality fonts now that I don't see this as being an issue in a school setting. And it's easy enough to fix if you know what you are doing.
b) run too many applications at once, causing the VM to thrash. Then they see the beachball (which is the OS showing the user that it's paging stuff in and out of VM) and think that their app is "freezing" and they force-quit the app, or worse yet, warm-reset the machine. This can cause application preferences and other system files and logs to become corrupt. This is where Onyx and Disk Warrior comes in. Onyx is free and fixes 90% of problems like this. Disk Warrior is the "bigger gun" and has to be used in more intractable cases.
One would hope that some basics of computer "dos and don'ts" will be covered in the curriculum.
7) Your "political" points are a reach. Reallly.
8) Linux might be a valid choice for all the same reasons that the Mac is. However, you'd then need to dictate a hardware platform - not all Linuxes are equally adept or have drivers for all hardware, especially in the laptop realm. Then you've got the issues of setup, configuration, maintenance, and so on to consider. Factor in the man-hours for that, and the Mac is clearly the "cheaper" platform. As a plus, you ARE able to walk into a store and purchase software for a Mac if you want to get out of the free offerings that Apple bundles with the OS.
9) Music - I dunno - I watch a lot of movies, and I watch a lot of the "special" content and whenever they show the composer or sound effects guy (whoever it might be) there is ALWAYS a Mac front and center in their setup. I don't know anyone who works in the music industry, so that is the sum total of my knowledge in this area. I do know that the Mac comes with Garage Band, which is a fantastic bit of software for music playing and creation, and it is deep enough that it could be used in a music class setting without need to purchase its monstrously powerful bigger brother, Logic Pro. I personally dabble in music software on both Mac and Windows, and I've not seen anything like Logic on Windows.
10) I'm very unclear on the point you were trying to make about media file sharing, but, on a Mac, if you want to go the Quicktime route, there is Perian - a free "plug-in" that allows Quicktime to play most codecs and containers found in the wild. Beyond that, there is VLC, also free, just like on Windows and Linux. Stuffit has nothing to do with video playback - its an archive expander (and not a very good one at that).