It's a good point about living in a hot climate often being associated with living a happy life. Although to what I've seen, there isn't much evidence for such a correlation.
In a warm climate you see people walking around feeling comfortable.
In a cold climate, the people you see are freezing.
The point about hot environments is true, but people are not anxious and your body rarely hurts. They are lazy and their minds blank out. It is often too hot to do anything except try to scam anxious northerners and move away from mosquitos.
You're right that once it gets over +30°C or so, you'll be miserable whatever you wear. But there is a large temperature range below that that is wonderful. The Bay Area is almost always in that zone.