Don't talk to Strangers

I was sitting in the station in Union Square waiting for my K train to go home when a woman carrying a lit stick of incense asked me for money. $2 to take BART. I said, "sorry," and she said, "Don't ever have children," to which I replied, "Okay." I don't typically give money to beggars in San Francisco. I feel as if I can't tell if I'm really helping someone or just perpetuating the high incidence of homelessness and panhandlers in this city. Sometimes I think I'm desensitized to seeing people in raggedly clothes who smell of dumpster and body odor. I work downtown so I encounter panhandlers on a daily basis and each time I think, if I give one person money do I have to give others money, too? If I'm not, how do I select who to throw a few coins over to? Whoever looks the most dirty or disoriented? I feel as if I don't have the answers. I don't even quite understand the problem. All I know is that sometimes, I just want to say no and move on.