I want to weigh in on this MMR talk surrounding supporting. I am not a good player by any means, but I play at a higher level than my friends and it's impossible to not notice some of their frustrations surfacing here.
No, Juice is not raising his account quickly through hard supporting but it's silly to think that he would be unable to do it at all. Yes, he would likely have more loses and yes it would likely take more time to raise his ranking but he would not be stuck in ELO hell if he was good at the role.
From my experience, it is a really bad mindset to classify yourself as "a support player." Too often I see people who end up in the role or pick it from the start and automatically assume "well, I'm just going into autopilot and will make sure wards are up and sit behind my carry so he doesn't die and I'll get a win."
Not only is this bad supporting, but it is making things harder for your team. It gives large advantages to the enemy if their solo offlaner is able to out level you and your carry as well as get decent farm. You are losing your lane if you don't punish them for having that weaker lane especially since you're team is likely losing the lane where the solo player is affording an advantage.
I have a friend who solely plays support and he is atrocious at some of the basic mechanics of the game. He can't last hit to save his life and has to rely on spamming his skills to get cs. His positioning is always terrible, he doesn't understand how to control a lane, he's unable to stack/pull or find experience and gold when under pressure, no clue what items to purchase when he does accumulate gold to best assist in that match and has a poor idea of how to work in aggressive tri-lanes.
The fact of the matter is, he doesn't know how to support because he doesn't know how to play any other position.
The good Gaf players have already mentioned that you need to be just as good - if not better - at the fundamentals as a support player because you are playing at a greater disadvantage than your team's "cores." You don't have a lot of opportunities to get cs from a lane so you have to make sure all your last hits count. Your team generally can't afford for you to wander off and solo the jungle to make up levels and items as you probably have the highest early-mid impact skills and need to be available for skirmishes. You won't have items to increase survivability and mobility until the enemies have item advantages on you and you will generally have fewer levels than most of the players in the game. You can't afford to make as many positioning mistakes because it's a lot easier to punish you.
Thus, you need to learn how to maximize your time as efficiently as possible. But if there is really bad communication from your teammates, how are you going to know what your team needs if you aren't knowledgeable about the other roles?
You won't realize that your ward placement is suboptimal for the mid player if you haven't played mid and relied on that vision. Unless you have someone to coach or point out these flaws, the best way to figure out the nuance of supporting is to get good in the other positions.
Finally, if you feel that supports aren't capable of winning games then work on becoming really proficient with heroes like Chen or Visage who are able to get objectives and apply tons of pressure without needing the help of hard to co-ordinate, pants-on-head retarded pubbers. I've seen enough pro matches where games were won by their supports to know that it's a fallacy to say they can't win games through their impact even with under performing teammates.