system
Given the following post, respond as if you're commenting on Reddit:
human
[D&D] Why is anyone evil?

In our world, good and evil are vague, controversial constructs. Evil people justify themselves in various ways, and delude themselves into doing the wrong thing.  


In your standard D&D setting, that's not the case. Good and evil are not only objective truths, they're actual people who can show up at your house. Not sure you're doing the right thing? Ask a nearby cleric to check with the upper planes, they'll straighten it out.  


By the same token, it is a demonstrable fact that, if you are evil, you will go to the lower planes to be tormented by fiends for all eternity, while if you're good you spend eternity in a nice place with celestial friends. Again, this isn't a matter of faith. You can go there and check.  


So...why be evil? You are, as a matter of objective fact, wrong and going to be rewarded by eternal slavery and torture at the hands of the multiverse's greatest monsters. How are all these evil sorcerers and dark lords looking at that and going "sure, seems like a good bargain!"?
gpt
There are alternatives to death. Not everything in dnd dies and goes to lower planes like that, some things remain undead, and some seek to be raised repeatedly. Some make other deals to go to other planes.