Torrents are legal cause they are only a file type. Demonoid got shut down cause it was allowing the downloads of illegal things. Torrenting has always been legal. Go to BitTorrent.com and you will be allowed to buy and download movies with full authority from the MPAA. Along with songs with RIAA approval.
Torrents themselves are not illegal. The stuff that the torrents give you could be. Torrents are used to distribute Linux distros which are free of charge. How would that be illegal to distribute?
IT is only when you have movies that hjust hit theaters up for download via torrents does it start to become illegal. There are just as many leagl purposes to use Torrents as there are illegal. It is just that people only know of the illegal kind over the legal kind.