While I don't approve of ATH and meme posts either, I don't think flagging posts on Steemit will be productive or uplifting for the community. I suggest simply not up-voting it and unfollowing those who you personally consider repeat offenders. As for scrolling, it's not that hard to do. We need to allow community members to express their creativity and excitement through posts on Steemit. Implementing a policy like the one you suggest runs the risk of users eventually blindingly flagging any (even high quality) posts regarding price.

I think your Reddit suggestion is a great one, though!