So your advice is - to enjoy SF, stay in the expensive areas, and get a taxi if you need to go through the poor areas, or the parts where there might be homeless people?
Do people ever go to poor areas to enjoy themselves? Wouldn't that be some form of poverty tourism? I don't see any reason to lash out at the comment you're replying to. Saying "these are fun areas in SF (or any city)" is not a political comment. For all you know the commenter you replied to volunteers in shelters, and donates to charities that aid the homeless.
> Do people ever go to poor areas to enjoy themselves?
Absolutely! There are many poor areas in London (Whitechapel, Brixton or Dalston, for example) but the idea that you would have to avoid them is crazy. In fact there are great reasons to visit them - the best Indian or Pakistani food in the city is in Whitechapel, the music scene in Brixton is amazing, there are great clubs in Dalston if you don't mind the hipsters.
How has SF let things get so bad that there is a major area of the city that people are told to actively avoid because of all the homeless people?
Some of the best clubs in the city are in the Tenderloin. Some of the best music venues are in areas that are "questionable". Same with the various theaters, the symphony, the opera, etc. They are always packed with people. People who live here don't have an issue going to those places.
I think you're reading the parent's comment in a particularly negative light. My take-away was along the lines of "take a cab, because it's too far to walk".
I might disagree slightly in that it's easy to hop on metro or BART from the Mission, but if you're in the marina I think taking Uber downtown is totally defensible. Hell, if you're new to the city and don't feel like mucking around with public transit taking a cab is a pretty routine thing to do.