Once advertising companies wrap their heads around what Steemit is there will be a lot of soiled underwear. Steemit may well become the largest social media platform in history... and it needs exactly zero advertising to thrive and grow.
That said, greed makes the world go round. Dolphins and whales will soon be getting solicited to post and upvote advertisements and it will be up to the community to decide whether to support or shun them.