Yes. It's not the software, to download torrents, that might harm the OS, but the torrent itself, if it contains malicious code. Depends on what you're downloading.
I was downloading on my old pc but i didnt give a **** about the possible risks of viruses, troyans etc. But now im more concerned wow i think that Apple inc deserves sth like a price or a bonus from the government (in the form of tax reduction) for encouraging the consumers to buy and use certified software, music, videos etc