> is it evil just because they are better at it than others?
It really depends on scale and proportions. In this case the exact boundary when something becomes recognized as evil doesn't really exist. The more efficient you will become on finding out weaknesses of other humans and using them, the more people will consider your actions to be evil. Displaying a picture of happy family drinking coke won't shock anybody, but suggesting discount on alcohol to alcoholic might come as wrong to many people.
> No one is forced to use FB as far as I know.
With facebook actively scraping phones for contacts, calls and messages, embedding widgets on third party sites and what-not. in a way we all really are forced to be facebook users.