[necessity]

Facebook is a company, a superfluous one even, no need is forcing you to use it and there is no need for it. Don't like the don't use it. Don't like tracking configure your browser accordingly and get a blocker. It's easy and free.

[icebraining]

You can't block if you don't know it happens (or that it even can happen), which is the case for most people. Very few people understand the concept of third-party tracking - nor should they have to.