I think there is an important distinction here though... we don't choose to have the ads thrust upon us on those other platforms. The ads on Youtube delay me from the content I'm actually on... the ads on Facebook, Instagram and Twitter delay the content of my friends from being shown.
Ads will absolutely appear on Steem, but it will be on content that we choose to click on. Or, some vloggers might talk about products/services in the middle of their content, but we can still choose whether to watch them or not.
What I see happening is companies or famous CEOs jumping on Steem and investing in the platform... and then upvoting content that speaks positively about them. A $10,000 upvote for my post about how Coke tastes better than Pepsi, the Blockchain would be overrun will copycat articles.
Regardless, we can still choose the content that we view, and that's the power of Steem over everything else.