With IRC around for nearly two decades now, which is real time text based only communication at its best, you should mean that Second Life has learned from it and that groupchat in Second Life si reliable und useable.

This is often not the case. Why? Because compared to IRC Second Life has many pitfalls and annoying things, which IRC has already mastered. Some of those annoying things are:

• Sending messages to a big group is still unreliable. You normally need several tries while the discussion moves on and on, so it is very hard to contribute to a real discussion at all.
• It is not possible to moderate a group or close the group chat at all for the public. This means, only some people with a certain flag can speak, the rest can try to type something in but it will not be shown at the channel at all. IRC has such a thing, it’s the +m (moderated) flag for a channel in addition to the +o (operator) or +v (voice) flag for certain users.
• It is still not possible to mute channels. When you want to be in the channel for announcements and notices of the creator but don’t want to hear the chatter of the crowd in it, you’ve got two choices only at the moment: take it and try not to get too annoyed or leave the group in the long run. Of course, when the group is important to you, you get annoyed more and more easier over the time.
• Since always people without good knowledge join groups and use the chats to say "hi" and so on, which most regard as spam, often short conversations happen at times when you cannot handle it or need it, popping up and annoying you to hell. Ignoring this would be the best case, but no, there are always some who make the conversation longer telling how bad this behaviour is on the group chat, calling it spam, whatever, fueling the discussion even more.
• IRC clients work channel based, meaning you get only the messages of channels which you’ve joined before. If you haven’t joined a channel, you don’t get the messages at all. Second Life works also channel based, but you’ll get the message as soon as someone sent it to the whole group.

To sum it up: public channels, especially big ones, in Second Life are pretty useless and often annoying as hell. If you really want to reach your broad audience, better switch to other means of communications. Second Life has some design differences to IRC. IRC itself is a proven and reliable way to communicate with masses, the biggest nets like Quakenet have got over 180000 users at peak using it every day. And those counts are not decreasing despite the other means of communications.

So to learn from this proven and reliable technology, how to manage big masses and to adapt those concepts, if possible, would be a very big step forward for communication in Second Life, be it text or voice based, forward into the right direction.