The guy's a dick from the 'holier than thou' camp. You can get viruses from just as many legal sources. I've seen over 300 trojans and spyware programs on some innocent noobie user's computer, and all they did was use the anti virus supplied with it (Norton) and take it on the internet (and it got fixed after that without formatting).
P2P is a better way of downloading big files quickly than client/server, and plenty of people use it for linux distros, patches, demos and free programs. Unfortunately the big download sites don't use it despite the fact it's more efficient, and to use nearly all of them you need to give your email and get spammed or pay them to get decent bandwidth. The files are legal, but without the original source providing hashes for p2p you can't be sure it's a good version, or just something uploaded to give you a virus. There are plenty of people other than those protecting their IP who upload viruses, and a lot of them upload anything useful, free or not.
My advice? Get an old 10gb hard drive and put a clean install of windows on it (saves learning linux, and gives you more tools you can use to fix an infected windows drive, like windows AV and anti spyware programs).
Viruses can only be inside files that are 'run', that includes the boot sector and core startup files of the operating system, .exe and .com files of programs, .dll files, and a few others that have executable parts like .wma and .wmv files, or office files with macros, and saved web pages that do stuff with activex and javascript. Most files are perfectly safe, just being data that can't be run, and all files with viruses are safe to mess around with so long as they aren't run.
Boot off your 10gb drive, install a free AV program (only take the bare install to google, then the AV program's website and it should be safe enough to take on the web for that job. I'd recommend you get both Avast and Grisoft's AVG, as you're more likely to find everything using more than one program), then shut down and reboot with your 10gb drive as the boot drive, and your infected drive as a second drive in the system. Now you have full read and write access to the infected drive to fix it with your AV program, and so long as you don't try to run any programs on it nothing else can get infected.
If your 10gb windows install gets messed up you can just reinstall it without losing any important files.