It's safe to say that Autofill is the most hated part of League of Legends. Most players would rather face down a 12/1 Katarina or have their first jungle camp stolen by their ADC than be forced into the most dreaded role in the game: support. The role has always been the least popular in the game, and it's not terribly hard to see why. In a game that is often exalted due to the awesome plays that are possible in it, the humble support role often falls by the wayside. One of League's most eternal questions is why a player would want to be bound at the hip with another player that they have to babysit? Solo queue is too often about which individual player can snowball and carry the team on their back, yet the perception of the majority of the League community is that supports simply can't snowball in the fashion.
That, frankly, is idiocy. Anyone who could seriously believe that has clearly never played against a truly competent, at least in this day and age. The support role is no longer the sole domain of passive healers like Soraka or Nami, but rather is now home to a diverse cast of champions that include mages, tanks, and disruptors aplenty. It's true that a support will never make a flashy assassination like Zed outside of the most absurd circumstances -- I seriously doubt that anyone reading this hasn't been blown up instantly by a fed support Zyra at some point over this season -- but that doesn't mean they can't carry. Leona might not be able to assassinate people like Zed, but you know what she can do? Gank the enemy Orianna so often that she's more used to seeing a gray screen than a colored one. You may not be able to split push like a Jax as Tahm Kench, but you sure can enable some crazy split-lane hijinks for your team courtesy of Abyssal Voyage. Sona's Cresendo might not do as much damage as Command: Shockwave, but a well-aimed Crescendo ends a teamfight just as decisively as any Shockwave could.
If you go into a game thinking that it will be impossible to carry, you're likely to just fall pray to a self-fulfilling prophecy. The trick is to find supports that match the playstyle you enjoy elsewhere. Are you a top laner that loves to lock down enemy targets and take hits for your teammates? Try out Leona or Sion, both of whom might as well be top laners if they ever get fed. Is AoE burst damage more your style? You're in luck, since Zyra still remains one of the strongest picks in the game. Do you love to roam around the map and set up plays all game? Bard might be worth putting some time into, then. Support is all about finding the kind of champions that match the way you want to play the game, and once you do you'll carry just as surely as if you were in your preferred role. Don't be the autofill support that every team dreads to have on their team. A handful of games will go a long way to help you win those one in ten games where you get banished to the bottom lane, and that may well make all the difference in helping you reach your target rating.