The key reasons for homelessness are mental illness and/or drug and alcohol addiction. Ordinarry people whom are not subject to these conditions tend not to become homeless because they are rational and no matter how bad things get they will find a way to provide a home for themselves, even if it's a humble one. For the others who are subject to substance addiction, Their addiction takes over their entire life. Their priorities are to get their next high, not to provide a home for themselves. For those subject to mental illness, they often have drug and alcohol dependence as well that may be the root cause of the mental illness or the only way they have found to cope with it (self medication) that often exaserbates their illness. The vast majority of homeless are not dangerous. I will agree however, that it's impossible to tell which are and are not untill confronted with one that is. You can control your exposure to dangers by avoiding stupid places at stupid times to do stupid things. For those times when you are not doing something stupid, at a stupid place at stupid times when dangerous people find you, we have firearms.
For the record, the Las Vegas Strip at night is not a stupid place at a stupid time. Though people often go there to do stupid things. On the other hand, it's not hard to end up in stupid places like Highland Drive, or Koval Lane because people who don't know better might think these places are just extentions of The Strip. The same is true for Downtown. Freemont street is generaly safe, but it isn't hard to wind up a little farther east of the covered area where you can find yourself in a whole other world of danger and risk. For those of us who have lived in Vegas for any length of time, we're over the "allure" of the Strip and we avoid it at all costs. It's a tourist trap where everything costs at least 3x what it should, and many of the people there are obnoxious and drunk.