As someone who lives and works in SF, I think it depends quite a bit on your social scene and neighborhood. Where I'm at it's constantly alive with people in the parks, out for running/biking groups, going to farmer's markets, attending art fairs, bars overflowing, etc. I meet lots of interesting people and enjoy the scene quite a bit, but maybe I run in a younger crowd than your friend who complains about the city.

Not here to change your mind, but I'm "defending" SF because I've never experienced such a difference between the lived experience in a city and the online vitriol you see constantly about it. It's a true "don't believe your lying eyes" situation and it's honestly a bit disorienting.