well..I see a couple of problems.
1. There is the obvious problem where you accidentally shoot someone who is chatting because you don't immediately see the chat icon above their head
2. The second issue is when the chatter decides to chat in the middle of action or while they are sitting in their base...and you come in to take their flag, but you ignore them because they are chatting. Then just as you are about to leave with their flag, they decide to start attacking.
Now, obviously, that isn't fair at all.
So, perhaps there could be a server setting to setup some rules for chatters:
1. Make them invincible while they are chatting
2. But, make them lose the ability to fire or use their grapple for 3 seconds after they are done chatting
3. And...have none of the above if they are holding the flag. If they are a flag holder, all bets are off. They don't get the right to chat.
That would at least allow some options for dealing with issues of chat-fragging / text-fragging / type-fragging / talk-fragging (whatever you want to call it)