Uh what? That individuals consume some amount of resources to live doesn't mean that they live comfortably. There is going to be some kind of minimum amount you have to pay to live, as you can't get everything for free even if you are homeless. That even those with the lowest incomes use up resources equivalent to $20k per year doesn't mean that those people are living comfortably, but we can see for Americans that there is some kind of minimum cost to living even if you can't make enough to pay for it all outright.
Drugs and poverty are intersectional. Laws for drug offenses involving substances most prevalent in poor communities have and continue to have harsher penalties than for drugs that are prevalent in more affluent communities. Drugs are highly available in poor communities, both for addicts and for those that want to sell them since economic advancement through traditional channels are denied to them. Police agencies in many cities enforce crime in the poorer parts of town that are inhabited primarily by people of color much more often than in more affluent areas.
The effects of drug prohibition amplify exiting social and economic issues in US society, so we know that US drug policy has been a total failure and must be changed.
There is actually a lot of research suggesting that inequality in a society is itself the cause of many problems. This is not surprising to me, since, after all, it is ridiculous to speak of wealth in absolute terms. $20k doesn't mean anything.
$20k has a very well defined (albeit complex) meaning: it means that the sum of the prices of goods consumed by the individual adds up to $20k. (Note that the figures I gave for other nations were adjusted for PPP, so price levels are adjusted.)
I can think of no mechanism besides envy which would cause income inequality to harm anyone. It's not as if the US poor lack some good or service which is available in other, more equal societies.
Note that the Spirit Level only provides a correlation between inequality and other problems. It does not show the direction of causality.