Dropbox and Box are file syncing/backup services, and MegaUpload is a filesharing service. Both types have different legitimate use-cases. Youtube is also very much about sharing movies and music, but since youtube videos are publicly viewable, it's easier to monitor and take down. How is MegaUpload supposed to monitor a bunch of passworded "VacationPhotos.rar" files? Just because it might be a Hollywood movie doesn't mean they can take it down on suspicion.

There are music artists that have put their own albums on MegaUpload as a central place where anyone can come download. There are people like myself who put a collection of high res photos in an archive and hosted it on MegaUpload for any of my family or friends to download. Analogizing MegaUpload to an assault rifle is saying that there's no reason for civilians to have access to it, where there are actually many legitimate use cases for using a filesharing service for mass distribution.