Every other competitive game can handle voice chat, though. At this point, even Co-Op games have had voice chat for years. And I've never heard of anyone ever being flamed for not using it, even back when I played high level CS:GO (MGE/Roughly Diamond). CS:GO requires way more active call-outs than League and doesn't have a ping system, so voice chat is way more necessary, but you still never saw flame. In fact, I'd wager a lot of the flame comes from the fact that text chat is so much worse than voice chat. People are way more willing to insult using type than speech and everything seems like flame without the inflection and accenting in voices. Plus, voice chat might help bridge the gap between soloQ and pro play, making it easier to balance champions like Ryze.
In any case, I'm rather disappointed to hear from a Rioter that it won't be happening. I was under the impression that it was a WIP that was coming relatively soon considering the addition of pre-made voice chat...