Originally Posted by March of Dimes
Your role as a support is not to sit there and spam a heal. You need to have a large presence in lane, and you need to stay relevant later the game. A good support can either act as a kill lane, to completely crush the opposing lane, like Taric, Leona, Jarvan, Fiddle, Blitzcrank, or can harass the poor enemy out of lane, like Sona or Lulu. Then you have the bad supports that can only tie at best lane by babysitting: Most Soraka and Janna players. The other supports can babysit while doing everything else.
You can't force objectives if you're tying a lane. You can't build up that much of an advantage at all if your goal is to tie the lane. You won't get a dragon if you can't create an opening.
Later in the game you need to bring utility to a team, and, this is especially true in solo queue since everyone else is going to want to be on the offensive, you need to protect the AD carry. This doesn't even need explanation. Look at how Janna can protect an ADC and control a fight to make up for her babysitting lane. Lulu. Leona. Alistar. Blitzcrank's game winning grabs.
Now look at Soraka. Hurr 100 armor for 3 seconds. That's not going to stop Irelia from bashing the ADC's face in. Taric is weak in this department too, but he's also one of the best kill lanes around, and provides team wide armor and an offensive aura.