Well Youtube Downvotes are nearly the same as Upvotes, it just changes the to whom the videos get pushed, exposure will still be increased. There is no punishment that people can do to others by downvoting them. That is the reason why Hive can not grow without bribing it's users on the Social Side, people offboard each other with automated downvote trails.

Ads on or off is not important actually, even if that is a valid point. Especially for the curious case of Instagram, which is basically 90% ads at this point. The raw numbers of using it for socialization by expressing themselves in some way, shape or form is what makes it a Social Media Platform.