You get an upvote from me, not because I like the idea of ads, but because you bring up the first question I had when I joined: Who's paying for all of this?
The answer I arrived at is that the people who are buying STEEM at Bittrex and other exchanges are paying for this. They are taking a long position in STEEM, i.e. they believe that STEEM will grow in value over time, and would like to make a profit.
We could probably get rid of most of the leeches if, in addition to requiring either a Reddit or Facebook account to sign up, there was also a requirement that your Facebook account is over a year old and has seen some use, or that you've actually got some karma on Reddit.
I'm also fairly selective about which posts I upvote. They either have to be well-written and have a reasonable length to them, or they must bring up an important issue. All of Steemit won't be doing this, so yeah, we'll need anti-leech mechanisms. (Welcome to politics.)