On one hand there's a horrible standard that's placed on women to "be pleasant" and smile. I'm against that. I'm also against telling people just to smile when no one knows what the other person's day or life has been like. And some people have issues with depression.
On the other hand, what is life without joy? I truly believe that happiness is a choice. That doesn't mean one goes around grinning like a game show host, but it doesn't mean they have to be a sourpuss either. There are many methods to manage depression and it's healthy for those who are afflicted to find the right one(s) for them.
I'm friendly to almost everyone. Those who have met me understand. I go out of my way to connect with a person and to make them feel valued and comfortable. I've often provided a shoulder to cry on for people I've just met and I'm happy to do that. Sometimes people just choose to be unhappy all of the time for the sake of it. Those people, keep them the heck away from me because they often suck the air out of the room like a cancer and I don't need to be a part of that. It's important to point out that's the extreme, not the norm.
There's also something called smile therapy. It sounds stupid and cheesy, but it has been proven that the simple act of smiling can often improve one's mood. And once a mood is improved it's easier to maintain.
So, I guess smile if you wanna. Be yourself. But it's also important for every person to ask themselves what their giving off to others in the world. All of us here admire Jim Henson and that was the core philosophy of his life's work. Fraggle Rock taught us that life is symbiotic. Sometimes we need a Boober. Sometimes we need a red. There are times that the Boobers of the world have a responsibility to shrug off their angst for the greater good of their friends. Sometimes the Reds of the world need to have an appreciation for the unfortunate things that can happen.
But in the end, in the bigger picture, we all play a part to create balance. The question shouldn't be about smiling or frowning (and just because someone's not smiling doesn't mean they're not happy just as a smile doesn't necessarily indicate true happiness). It's about how we treat people, how much we take and what we pass along.
PS- But not smiling because it would "disappoint your fans" is a completely ridiculous reason and is a red flag to me that Miss Stewart is not likely a person to take seriously.