MU provided filesharing tools. People used those. That is not inherently illegal and I use similar tools from other providers myself.
What MU did was knowingly permit people to also use their tools for purposes that fell foul of various countries' intellectual property laws. They did not abide by the legal process established for ISPs and hosting companies to remove content found to be infringing.
They actively worked to obfuscate copyrighted material, make the DMCA process very difficult to go through for copyright holders and make it as difficult as possible to actually get material completely deleted from their servers (they often just removed the link to it, thereby just hiding it and allowing the uploader to create a new link and re-share it).
They had an internal search engine where employees could search through and download this material from people's accounts, and emails obtained as part of court proceedings confirm employees knew full well what they had and what they were doing. Plausible deniability only goes so far.
They sold paid accounts for priority and express downloading and returned a portion of the money to the uploader - so both the uploader and the service provider were directly profiting from breaking the law, and they did all they could to carry this on for as long as possible. Unethical, immoral and illegal.
Biting the hand that feeds IT
