I see lots of companies offering competitions where you have to comment on a post and sometimes tag a friend to have a chance to win something. If instead of do

I see lots of companies offering competitions where you have to comment on a post and sometimes tag a friend to have a chance to win something. If instead of doing that they required people to signup for their newsletter, then they would use Facebook for farming new subscribers, which is a relationship they own (they probably have to pay for the sending service, but that is like me having to pay for gas: I am not beholden to a monopoly).