One of the debates you will here often surrounding street photography is about its moral nature.
Many street photographers publish or sell their work and find themselves and others questioning whether it is right or wrong to profit off of their subjects. This subject comes up even more often when photographing people who are considered "less fortunate".Of course these arguments often ignore the fact that many street photographers help the downtrodden by bringing attention to their plight and rallying support for them.
However the question remains, are we as street photographers exploiting people?
What many people fail to realize is that ethics like so many other things are individual in nature. People have their own sets of ethics influenced by their upbringing and life experiences. What is ethical for one is heinous for another. So individually the ethical nature of our photography hinges entirely on the intent and goal of the photographer. If you are trying to take advantage of others then yes you are being unethical. However you can profit off of street photography and still be totally ethical. It is simply in your mindset.
Consider the work of Bruce Gilden who is the most divisive street photography out there. When people question his work and method they dont just question the way he operates. They question his intent, his goal, his way of thing. A photograph never stands on it's own. The photographer is always standing there with it.
When it comes to street photography as a whole asking whether or not it is ethical is simply an empty question. Street photography is documentary in nature. It can be likened to writing a history book. It is neither right or wrong to photograph any event on the street or any person. It is simply a recording. It is fact (unless heavily modified so as to no longer represent the actual scene).
While one may feel bad for photographing the homeless it is not bad to do so. They exist and should be documented. If you find youself having a moral dilemma then next time you decide to photograph the homeless try talking to them and maybe even buy them a meal. They are people like everyone else. They will most likely appreciate the fact you treated them like a real person.
When you or others begin to question the moral nature of your photography simply remember that street photography has no ethics. It is neither right nor wrong. The photographer is the one with the ethics. If your intent is to record and share and help people with your photography it can be called nothing but good. If your goal is to take a photograph of a homeless person to get more views on instagram then maybe you should rethink your values.