Pretty much summed up in the title.
I actually think this is one of the most prevalent forms of toxicity in the game, it happens almost every game by someone who feels aggrieved by another player doing badly, or is just used to blame your team mates.
It'd be nice if asking others to report was stated by riot as unacceptable community behavior, as it promotes player bullying and is generally an unpleasant thing to do.
I understand people being frustrated and that sometimes players do indeed intentionally troll, or go afk. However the decision to report other players is a personal one, and should be made by individuals. This would surely cut down instances of false reports, flaming and generally make the game a little more bearable for people who make mistakes.