The vast majority of chronic homeless people (stunk, dirty, massive backpacks) have drug addiction and/or mental illness[3]. They also make a boatload of money (often > $100,000/yr). The problem is that they lack the skills necessary to effectively use that money and reintegrate to normal society, so they're relegated to homeless life. Homeless life isn't easy either--most of them have either been around someone who's been shot, or been shot themselves. Rape is prevalent, for both genders, but especially women. [2] Life expectancy is not good[1]. In talking to hundreds of homeless people, I have only met one homeless person who was there by choice.
Having a Starbucks cup doesn't mean that they have piles of money. It means they received > $4 in donations recently and were able to spend it. The money they earn usually quickly goes to drugs, alcohol, theft, or impulse purchases. This is why it's so key to NOT give them money. You or I would be smart enough to put the money in a bank, save, and get back on our feet. They can't (or they would have already done so).
When I walk down the street and run into a homeless person begging, I offer to take them to a nearby fast-food restaurant. About 50% decline, and the other 50% are immensely grateful. That allows you to engage them in conversation, and offer them to take up a rehab program, which can teach them to break their addictions and gain the life skills they need to become part of society again.
[1] young homeless women are four to 31 times as likely to die early as housed young women (O’Connell, 2005)
http://www.nationalhomeless.or...
[2] In yet another study, 9% of homeless women reported at least one experience of sexual victimization in the last month
http://www.vawnet.org/applied-...
[3] According to Didenko and Pankratz (2007), two-thirds of homeless people report that drugs and/or alcohol were a major reason for their becoming homeless.
http://www.nationalhomeless.or...