It just feels weird when hero is the only one who is silent. And it's also very limiting for cutscenes. I don't really get how somebody could say that they would do such thing for immersion.
Honestly, in an RPG I find the humbler presentation the better. Partial VO or no VO at all works the best for me. Here is why:
RPGs are all about creating your characters and interacting with enviroment. The more defined those interactions are, the less room for maneuvering there is. BG2 is not terribly big on choice and reactivity. And yet I was able to make many playthroughs, with various characters and they all felt differently - in a big part because there was a decent amount of blank space through which I could express my character - filling his voice in my head was one of those.
Have Witcher3 or Mass Effect or even Gothic... because how defined the characters are, I don't find subsequent playthroughs interesting. Especially the first two... those are barely RPGs. More like action games with some RPG elements infuesed into them. Shepard will always be out of my control.
I agree that, if you use movie style presentation for everyone else but your character, there is discrepancy there. But while devs managed to create customisable avatars which can act and interact with enviroment... how do you do voice? For that reason I prefer my RPGs more abstract, with top down view, getting the imagination working, but not defining it more then needed.
