I agree, we shouldn't have to walk over bodies, their belongings, trash, etc. to walk down the sidewalk. And you're right, that is behavior. But again, I don't think that everyone downtown with that kind of "screw you" attitude is necessarily homeless. Which is why, in my mind, the focus needs to be on behavior. Are the two related to some degree? Sure. But homelessness in cities is a fact of life. And I don't see how you can legally ban anyone (or should) from being on public property during daylight and evening hours if they're not bothering anyone and not causing a mess.   
I worked downtown for a portion of the 80's and 90's helping to maintain the public areas. We cleaned up a lot of  "stuff". Some of the people who appeared to be homeless weren't a problem. We even got to know some of them. Some of the younger "kids" is where we had most of our problems. Of course, things have gotten a lot worse with drugs, mental illness, etc., and just the sheer number of people downtown.