Why is opposing team allowed to report such things as verbal abuse?

I do not understand why the opposing team is allowed to report anything other than an obvious afker. The game I was in, the opposing team made a deal that they would report me for intentional feeding (simply because I had the highest deaths at 11 but every other player had 8 or 9) if our team reported their player for "verbal abuse." Of course we could not see their chat so how can an opposing player report for such a thing? Why is this even allowed as I would imagine it creates mostly erroneous reports that Riot then has to sift through? Let me just make one thing clear, I am not trying to complain about the report against me, I know when reviewed it will be ignored, for lack of better words. I am asking why an opposing player/team can report at all, other than an obvious afk? Everything on the list, excluding leaving/afk (and then only when their level is 1 or 2 or MAYBE just way less than everyone else), cannot be determined by the opposing team. Am I the only one who thinks it's asinine that a player on the opposing team can report for "verbal abuse?" Our enemies even went so far as to make a deal at the end of game, isn't this the very definition of nonsensical?