I guarantee you, they ask themselves that. Why don't you try asking yourself why a street kid would bother to ask douchebags like you for anything if they didn't really need it? Many (not all, granted) of these kids opt for homelessness because the hellholes they called 'home' were no longer viable options due to escalating incidents of sexual, emotional, and/or physical abuse. So, the next time one of these 'junkies' asks you for something, perhaps you should turn that keen sense of judgement inward and reflect for a moment on your own lack of empathy and why you can't bother to spare even a single fucking cigarette.
@UnToward - It's not about empathy, it's about marketing. It's called knowing your audience. So for for lack of evidence to the contrary, I'll conclude that the leeches are the sum of their own selfish decisions and lack of self awareness that they appear to be.