Opinions on facial expressions would be a silly thing to get upset about. However, I read that your hypothesis is that all emotional responses or facial manifestations thereof should never be a willful act, and thus are entirely subconscious. I find that to be a position that is hard to defend, if for the least of reasons that the consciousness of many actions is often not black and white.

In many cases I choose the facial manifestations of my feeling, in other instances the emotions are strong enough that I do not. In daily life I choose to smile for the same reason I choose to shake hands when I meet someone, or the reason I make eye contact with someone I'm talking to. Smiling is just something humans do to interact, and if my smiling can make someone else feel better or more comfortable (myself included, which does happen), then I'm happy to do it.

Edit: Further, I stand by the statement that looking for smiles on others, regardless of conscious/subconsciousness of them, has important diagnostic value. People can see whether someone has a good disposition or not. Whether the smile is entirely subconscious or entirely conscious (again, this distinction is hardly so black and white) does not matter much when examining whether this is someone you want to interact with. If it is a subconscious smile, then life is going good for them (at least currently) and this is a person you may want to share experiences with. If the smile is conscious then this person makes an effort to enjoy themselves, makes the best of situations, and is looking for positive social interactions, just like you doing the diagnosing.

As I know neither of us will give any ground on this, however, I amicably accept your disagreement, and offer the last word.