I think this is a little over-broad. As written, the only way to be good is to stop all evil everywhere. Or am I missing something?

If while acting in your own self-interest you knowingly, through action or inaction, allow others to come to harm, even indirectly, that is evil.

I think most Americans buy products made via unethical labor practices, and which damage the environment, harming everyone.

Are you really making the argument that the vast majority of Americans are evil?

By that description, the vast majority of people are evil. Well, both evil and good, since most people at least occasionally do things that aren’t in their self-interest to help others. But primarily evil, thanks to the inaction clause on the evil side and nothing comparable on the good side.

They’re also more evil the more educated they are, since they’re more aware of ways that people are suffering harm that they could potentially abate.

For example, if you are not homeless and you are aware that some people are homeless and a storm is coming, if you don’t help them all find shelter - to the extent of bringing them into your own home even if it means you end up not having a place to sleep - by your definition, you’re evil.

I’m not a fan of that definition, either for D&D or anything else, but if it works for your table, great!

No. Neutral only cares about the cosmic or universal good. The welfare of others or ones self doesn't factor into it. Many druids are Neutral because the balance of nature (the natural order) is the motivation behind their actions.

I like your take, you said it better than I did.

I disagree. Lawful or Chaotic describes ones adherence to rules; either those of society or their own moral code. Chaotic would describe one who does not adhere to any rules or guidelines; nothing is off limits except that which would violate their alignment on the Good-Evil axis. Neutral would mean that one would bend those rules to achieve a particular outcome. Lawful is going to stick to the book; they're very conservative.

Evil isn't the desire to harm others. Devils don't desire to claim people's souls for the lulz, they do it for power. Everything they do is to gain power, for their own benefit. They don't care if the souls will become lemures or a snack, they just try to convince people and scheme for their own benefit anyway.

Demons are way more brutal, they don't really gain pleasure from pain per-se, they also want power, but their approach is way more direct. If they can gain power by killing all those people and bathing in their blood, thay will forcefully do it, not by deceiving the human through a shitty contract, but by forcing their power.

Devils are LE, demons are CE. All in all, evil is the disregard of moral consequences when finding ways to benefit yourself.

Deceiving someone to sign a shitty contract so they now must slave away for you? LE.

Kidnapping someone and forcing them to do stuff to your benefit? CE.

Reaching a fair accord so that you allow people in need to work for you for a fair price, where both parties give a bit so no one is really getting taken advantage off? Either LG or LN depending on the context.

Offering to kill the bad monster that is terrorising the town for free, and disregarding the lucrative offers from it because it's the right thing to do? Any good alignment.

Any of those people could have desires of harm, it's how they channel their wants that puts them in different places in the alignment chart.