Is intentionally feeding bannable?

I know you've all heard it all a thousand times before, but it's incredibly frustrating playing in low elo. I can't count how many great games I've played where winning isn't ever even a possibility because someone on the team decides it will be a super fun time to die as many times as possible and taunt their teammates about it while doing so.

I'd say that somewhere between 10-20% of games involve a situation like this. Not even counting games with people that AFK or never connect, which is also a massive frustration. It makes it virtually impossible to climb when nearly half of your games are 4v5 at best.

Why aren't the people that go out of their way to feed being banned? I don't get it. I can't imagine that these are all first time offenders. Invariably they'll say something like "go ahead and report me, it won't do anything." And sadly, I believe them. I do report them, but I assume that most likely they're allowed to just keep doing the same thing and go ruin more games for a bunch of other people.

Shouldn't this be a 'one strike and you're out' type of deal? It's pretty terrible, having someone intentionally ruining ranked games for four other people. It makes the experience of playing the game nearly unbearable at times. Why is this so prevalent and why are these people allowed to keep playing?