how is not talking occasionally better? They're just mute. They don't feel "alive".
Not if you're just watching them, hoping they'll do all the work for you.
The silent movie comparison only works if you're a passive receiver of the game's content. Just like watching a movie, where you sit quietly and a story told to you.
But that's not how a lot of us play RPGs. We're trying to roleplay a character of our own construction (and a different one with each playthrough), and having the character already feeling alive does our job for us.
When roleplaying, we're not watching our character from outside, like we would when examining another person or watching a character in a film. Instead, we're inhabiting (and populating) that character's mind, experiencing his life from his perspective. We experience NPCs from the outside, but our experience of our character is fundamentally different.
Our relationship with our character should not resemble out relationship with other people; it shouldn't be a relationship at all. We should
be our character.
When I speak, I don't need to listen to what I say in order to find out what I said. And nor should I when roleplaying. When I experience an emotion, I don't need to watch my behaviour to find out how I feel. And nor should I when roleplaying.