First point; enough with this unrealistic ideal of immersion. If a chat roll does it for ya, there is something bizarre about what you think is "realism". We don't really have it in MMOs, its just not a real thing.
Second Point; you mean easy on top of the other super obvious ways we know an NPC from a PC? You understand this game makes us an NPC when we aren't logged in. We aren't going to be saying anything other then preprogrammed responses.
Third Point; Griefing how exactly? If you are talking abuse, open mics playing nonsense music or clips... Mute button. You have to mute or ignore the same a-holes in a chat window too. SPAM is SPAM, you can easily deal quickly with both varieties.
Fourth Point; Text Chat is the fall back. We have RP etiquette that is well established in many communities for people with no desire or ability to use VOIP. An MMO immediately creates external VOIP social bubbles regardless of who can or will join in. When the VOIP option is integrated it creates an opened end to those private bubbles and we see a marked increase in dual use VOIP (they still use a private channel but engage more with Proximity VOIP).
Having more options than less is only a good thing. I am only seeing nonsense and narrow excuses so far in all the many threads opened on the topic. If its not an option there'll be consequences... if it is an option there'll be consequences.
I would pose a question to those who seem to adamantly NOT want VOIP. What if they decide to include it, what will you do? Does it stop you from pledging?