Piracy is illegal. The reason is copyright infringement. Essentially, you are knowingly downloading and distributing illegal material when torrenting. However, the government doesn't really care if you download music/movies illegally because arresting everyone they can find doing it is so impractical. However, wherever they can they will shut down or block the site.
Torrents are files that are given out for free even if they cost money. If they are illegal, then why haven't they blocked the websites? Also, why doesn't the torrent providing companies get sued for illegal distribution of files and go bankrupt?. This is why I think Torrents are completely legal.
It is not technically illegal to torrent in the U.S. The reason is because you are simply sharing copyrighted material, not selling it. If you sold the copyrighted files, then yes, that would be illegal. But sharing is not. People share music, movies, games, and many other things through torrents because it is an excellent way to save money.
That being said, while it is not illegal, it can be dangerous if not done properly. First off, the downloaded files can be corrupted with viruses and malware. If you have ample security programs, this should not be a problem.
Secondly, and more importantly, the holders of the copyright for what you are downloading often take part in torrenting themselves. Why? Because by doing so, they have the ability to see the IP addresses of the seeders and leeches. Then it is a simple matter to call up the ISP of those people and make trouble. True, even though they probably wouldn't win a lawsuit should it come down to that, the threat of legal expenses, such as that of an attorney, are persuasive negotiation tactics in getting the ISP to act. That is why torrenters should use a reliable VPN, so that they avoid conflict.