Objectively, it's probably possible, and SpaceX has certainly made moves in that direction, what with Starship and the offshore launch platform conversion project.

But by 2029? Musk is either lying — which I see no motivation for him to do — or he hasn't an idea what he's talking about.

At most, maybe an empty, uncrewed Starship will smack the Martian atmosphere by 2029, and potentially even make a one-way landing. But the odds of that are low, IMO.

way more than 1,000 protestors plan otherwise

A bit, I suppose, but I think the difference is that bipolar disorder lets you still want to get better but hate the treatment that actually makes you better, whereas depression can make you not want to get better, period.

Ask them, not me.

If it works, it works.

Even if the depression's not severe, that depends on the depression.

If, as some have theorized, learned helplessness is a driving force behind depression, it might be that the person in question fundamentally cannot believe exercise can change their life for the better, regardless of what science or their therapist says, and that SSRIs (or psychedelics, or some other chemical actor) are what are needed to snap them out of it.

Depression is really a bit different from any other disease. Unlike most other diseases, the behavioral changes it causes can lead people to avoid treatment; a common cold or bipolar disorder aren't self-reinforcing, but depression is. Sure, certain mental illnesses might make someone harder to treat, because the behavior of person inflicted with them makes it harder for them to seek treatment, but few mental illnesses make people actively and consciously decide they should avoid being treated — like, "I know something's very wrong with me, but it's better for everyone else if I just crawl off into a corner to die", as opposed to a mere "I forgot where my meds are".

It's the great everything, really.

Speaking entirely anecdotally, exercise is also good at improving one's mental health, balancing sleep cycles and appetite, and, for some reason I'm sure there's a scientific explanation for, cutting down on acne.

With some notable exceptions, most of the human body's built around a hunter-gatherer lifestyle, which involves lots of exercise. All the stereotypical old-time talk about how people who aren't actually sick but just generally unwell "just need to get out of the house" and "just need some fresh air" is not entirely inaccurate.

Mind you, this doesn't mean that anti-Alzheimer's drugs shouldn't be developed. It just means that, currently, exercise is more effective than them.

Indeed. There's no such thing as Taiwan.

There's China, and then there's West China.