What you suggest is good for the overall community. However flagging some content just because it is a selfie - isn't a good idea.
Yes, posts which are crap. Meant to hoard upvotes by bot and cash in should be flagged.
Anything other than that - should be allowed. Because real people are sharing what they deem fit. So, I am on the fence. I guess I need to check more trending post to come to a solid conclusion. Lets see...