Can we talk about teamwork please?

So, something that has especially frustrated me with the new Legend of the Poro King map (but present everywhere else, of course) is this:

It takes five people working cohesively to win a game.

It takes one person to ruin a game.

What exactly are people supposed to do to give incentives to their teammates not to be that one person?

We're talking about that one person that instalocks without considering team needs. E.G. picking assassins on legend of the poro king, immobile ADCs (Ashe, Varus, Draven) on Dominion, and generally, not considering their team's needs, in both their champ selection, and their play style.

We all know those kinds of games, that we feel that we can only do so much, and when the game ends, we look at the scoreboard, and just see that one guy, or those two guys, who just wanted to have fun, their teammates be damned.

What exactly are some policies that could be implemented to drive home the point that when we queue up for a game, unless it's 1v1 snowdown, we are responsible not only for our own enjoyment, but the enjoyment of four to nine other players? Our four teammates deserve our best, each and every game. Our opponents deserve that we put our best foot forward, instead of wasting their time with a cakewalk.

However, as it currently stands, Riot's system instead is "it's completely alright to hang your teammates out to dry, we can't punish you for playing horribly, but we can punish anyone who reacts to you playing horribly", which I feel simply encourages there to be far more negative experiences for people than there need to be.

Simple things like instalocking (please discuss with your teammates if the champion you want to play may have a better alternative for what you want to do), selecting a champion you're mechanically deficient with for the level you're playing at (not everyone is Bjergsen, so there's nothing wrong with not being a mechanical god on say, Leblanc), and otherwise, being that one guy that drags down the team.

That Riot has very few ways of actually punishing the cause (being that one guy that brings down the team), but works so hard on punishing the symptoms (raging in chat) to me speaks volumes about how little they've done to actually solve this problem. People raging in chat can be muted. People who are clearly contributing to your team losing have far less recourse.

How exactly are we supposed to deal with this problem of those who absolutely refuse to be team players outside of "find four other buddies to premade with that you know will listen"?