San Francisco proper is one of the most diverse cities in the country. It is only 45% white. Over 30% of the residents are foreign born. These stats are from Wikipedia.
I lived around the corner from the Haight, too and I'm not sure what would make the area a "red light district." The hippie hill drum circle? Guys selling weed? American Apparel? Ben and Jerry's? The Gap?
The worst aspect of the Haight is the gauntlet of gutter punks between Cole and Clayton. It's actually a very nice, dare I say, "gentrified" area, aside from that particular stretch.
I lived in SF for 6 years and started to hate it, so I moved to NYC. I really like SF the city, and am one of the weird people who usually likes the cool weather. However, something about it felt like a retirement village for young people.
NYC is great but has its own set of headaches. I've found the tech scene pretty close to being on-par with SF if you're doing web or mobile, or even "BIG DATA". SV has a strong advantage if you're building things like routers, robots or electric cars. I miss TechShop.