None of this "old people are vulnerable" stuff or even the "tragedy of the commons" really matters as much as the demographics. If there were more homeless, (and if they voted), the old people would be forced to pay for everything for the homeless and put up with all of the noise and diseases and such without recourse until they left (if they could). Its less about what's "right", than it is about who is the majority.
Speaking of US demographics, have the babyboomers spent all the social security money yet? Isn't that set to run out just about the time that demographic bubble pops? A democratic republic might be the worst system there is, except for all the others.
The US Constitution was artfully constructed to avoid such tyranny of the majority via a Republic checked and balanced by various mechanisms (Electoral College, Bill of Rights, Separation of Powers, etc).
Old people on fixed incomes move the hell away from jurisdictions where the moochers of the FSA have a majority or plurality.
We still don't live in the dystopic unlimited democracy you posit, thankfully. That's why it's Time For Hillary! [*BARF*]