I have no doubt that there is a very dedicated audience out there who enjoys healing others. I don't doubt for the slightest that this style of support is what you prefer and would likely see.
From working on Lulu (and taking copious notes from Janna) - I can definitively say that Lulu only hits a subset of the support audience - because she has to be reactive or proactive in many of her moves - this makes the Lulu player feel like she's constantly being pulled by the game to accomplish an action (shielding incoming damage) or feels like she's constantly forced to do some other action that she doesn't want in order to be effective (I must harass with Q/Passive to get the most out of my character.) It's certainly an easier way of being non-toxic and interactive but it doesn't actually doesn't offer any lessons about how to make Soraka-like supports non-toxic to our game.
Soraka is a support whose mindset is definitely more towards Neutral - When things are at a stalemate - the Soraka player naturally incurs advantage over time. This is the both the fundamental appeal and the problem of her design - She does nothing to break a stalement - only incur bit advantages. Her current (heal) design - encourages a very high level of non-interactivity from the enemy team. This isn't about whether Soraka is fun to play or not - but whether or not she actually has forms of interactivity for her opponents outside of cooldowns. Cooldowns aren't a very noticeable or particularly engaging form of counter-play - effective but subtle and hidden. Is there a good way to play against Soraka outside of forcing cooldowns?
Support is inherently discouraging of interactivity from the enemy team as they're supposed to avoid most direct contact with the enemy team and focus on making their own team and team presence stronger, and I don't see how Soraka is any different.
I mean, is there a good way to play against Lulu and Janna outside of forcing cooldowns? Is there a good way to play against any ability-dependant champ outside of forcing cooldowns? Is there a good way to play against a champ with flash outside of forcing cooldowns?
Keeping track of what enemy abilities are or aren't on cooldown is a significant part of beating your opponent. Just like how I'm not going to engage on a Volibear until I've managed to harass him down enough to trigger his passive so when I go in for the kill, his passive is on cooldown. How is Soraka any different? You might say "You could ignite Voli during his passive." You could also ignite soraka or her carry when you go in on them, and/or use champs with more frequent grievous wounds capabilities like Tristana and Miss Fortune.
Hell, especially after the nerf to Soraka's infuse, Taric has better sustain potential in lane than Soraka. With Soraka, you can harass both Soraka and her carry so that she has to choose which one to spend her 20 second cd heal on, whereas Taric can simply heal himself and his carry at the same time, yet no one complains about his sustain, and he's even got a stun (typically much more useful in bot lane than a silence) and a +armor aura (whereas Soraka's ability to boost someone's armor is limited only to one person every 20 seconds). Soraka has more immediate burst heal potential (i.e. better clutch healing capability, which ya'll have said is what you want healing to be) and a better team fight presence in general, and that's the only reason that Soraka is used instead of Taric unless maybe the enemy team went all AD.
I'd much rather lane against an X+Soraka than an X+Taric.