One reason you should not use web applications to do your computing is that you lose control. It's just as bad as using a proprietary program. Do your own computing on your own computer with your copy of a freedom-respecting program. If you use a proprietary program or somebody else's web server, you're defenceless.

In the U.S., you even lose legal rights if you store your data in a company's machines instead of your own. The police need to present you with a search warrant to get your data from you; but if they are stored in a company's server, the police can get it without showing you anything. They may not even have to give the company a search warrant.

Facebook mistreats its users. Facebook is not your friend; it is a surveillance engine. For instance, if you browse the Web and you see a 'like' button in some page or some other site that has been displayed from Facebook. Therefore, Facebook knows that your machine visited that page.

Richard Stallman Quotes