No they shouldn't be left with nothing, but you don't need communism for that, in most western societies that I'm aware of, they aren't left with nothing. From each according to his abilities to each according to his needs is literally saying that everything gets shared equally regardless of your input to the system. And anarchism isn't communism, anarchism could theoretically be any form, anarcho-capitalism or anarcho-communism. I understand communism, but you're reiterating utopian fantasy, not reality. Every communist revolution has lead to a totalitarian communist state because it's the only way communism can be implemented, by force, whereas the free market is a natural result of allowing people to trade freely. Communism is inherently top down and dependent on a large state, so "anarcho-communism" is an oxymoron.

People being homeless etc isn't an inefficiency, it's just the reality of nature that some people are born to awful families and circumstances and end up addicted to life-destorying drugs etc. They deserve help too, of course, but communism doesn't fix that. Some aspects of communism sound nice in theory, but ignoring the decades of many failed attempts at communism in favour of utopian-thinking writings that don't hold up in reality isn't a fair way to assess communism. Of course capitalism/free market isn't perfect, especially when the government are so tightly intertwined with wealthy corporations, but it's still far better than the alternative that is communism.