Lets settle the "Forced to use" issue right now. Have you not played xbl.You can invite people to chat parties. Who said it would be forced on anyone? Having the option to invite people in your party or friends list into a chat party is hardly forcing anyone to chat. It is not an issue of why it shouldn't be implemented but an issue as why is hasn't.

Pro's
More options other than a third party program for chatting. (This also caters to multiplatform users.) As of now you must use a smartphone/pc and a third party to chat, which is archaic.
Easy to explain instruction and better end game communication.
Praise for FFXIV implementing something that should have been there day one. (I cannot think of a mmorpg/fps/moba/etc. in which in game chat would be a bad thing.)

Cons
Trolls
Having to deal with horrible people but thats what the mute button is for.


Point being we pay a subscription and there are no reasons why a chat function should not be added to the game.