This topic had been a huge conversation in the community in the past. There are those who are favor and at the same time, there those who really don't like it.
Among the reason why lots of people don't like to have ads in steemit is that they wanted to keep the platfrom free from those. They had already enough banner ads on every site they get in to but not steemit and they wanted to keep it that way.
If ads can help steemit reach its goal, then the platform might consider putting this topic on discussion again.