You don't believe, which I admit, is your option. However, with those student PCs infected with such malicious malware and viruses that they barely start up, let alone work. You can't clean such installation by Avast or whatever, those antivirus software is simply not enough. There are trojans, spyware and god knows what else, not just usual viruses that turn your files into folders, make them disappear all together or transform your PC into a hacked zombie for DDS attack. Granted, for macs its not that clean, but its not THAT dangerous.
Malware is far more prevalent on a Windows based computer than one which is OS X based, yes. But Macs are not invulnerable. If you know what has infected you, it can be fixed regardless of platform. There are plenty of issues that happen on Macs that have nothing to do with malware that require a reinstall, go to the official forums and youll see. Most Mac users I know think theyre invincible and at some stage they will get a very rude awakening.
That said I still prefer Apple Hardware/software. What I do hate is an Apple Fanboy.
(This is not a dig at you).