yet this kid who feeds intentionally and just troll picked mid in my ranked game
If he feeds intentionally and intentionally ignores his team's decisions he probably already has several reports against him, and will likely end up punished in the fullness of time. Riot's pretty good about banning intentional feeders, actually.
If you're banned as well, it's because you're also a bad influence to the team, and an unwelcome member of the community. Words from a stranger on the internet can ruin someone's game just as much (if not more) as a feeding teammate, and if you don't understand that than I, for one, am glad you've been banned. Both take the relaxation and gaming time of their teammates and turn it into a stressful situation that isn't fun in the slightest.
Sure, the person you verbally attack could mute you...but, on the flip side, you could realize it's just a game, man up, and deal with the fact that sometimes you get a troll or a feeder and just decide to have fun with the game and do your best regardless.
Long story short? Trolls and intentional feeders are bad news, and Riot needs to get better about banning them. But people who rage and insult their teammates are at least as bad, and, as you found out, Riot really doesn't want that sort of player playing their game.