I've never quite understood the desire to play an evil character. Considering the premise of the game is slanted towards heroic adventure, playing evil seems like you're just begging to be "that guy" who's going to disrupt the game and make sessions less fun for everybody else.
The slant of the game is, and has pretty much always been, for a group of trained and powerful individuals to go places they are not welcome, kill those living there and take their stuff to enrich themselves and enhance their skills in order to go to still further places they are not welcome and kill the residents there to take their stuff... ultimately to build a fortress with a standing army or even ascend to godhood.
Countless classic standard D&D adventures are built on the premise of either being a conquistador or a mercenary, and when they are not often the "call to action" to be a hero consists of proactively acting in one's own self-interest (the bad guys attempt to harm the character before the character gets involved) or if something noble is to be done, it is done with the specific offer of a reward involved.
Look at the standard adventure hooks....
You are in a tavern and someone gathers people offering to hire people for a task....
The bad guys have captured you and have you in prison, you must escape.
Your place of residence or a place you have business or connections in is under attack.
Honestly, a character that is particularly eager to commit violence upon others is WAY more necessary than whether the character is "heroic" or by any stretch of the imagination "good". You come to the table with a character unwilling or unable to use violence against others and you are just taking up space, getting in the way and failing to pull your weight during large sections of the game session. You come to the table with a character who is out to screw over every NPC they come across for the benefit and enrichment of the party, and they will be doing their job. People have come to this realization and jokingly call adventurers "murder hobos" because that's really what they are.
Now... as for the appeal of playing an evil character? There are a number of reasons.
Well, there are reasons why games like Grand Theft Auto are super popular. An open world where you can just randomly play out your darkest impulses and fantasies can be a spiritual cleanser.
But those cases are likely rare. The far more common reason is that it expands the number of options available to you. All too often there are cases where a puzzle or situation the DM comes up may have an economical, rational, direct workable, easy solution that would require minimal effort and comes with minimal risk.... with the problem being that it would require doing something evil in order solve it in such a way and you don't want to throw such creative solutions away simply because it is an immoral answer...
Or, alternatively, there might be times when your character's power can be increased, and thus their ability to have an effect on the game world, but it requires either doing or allying with evil to do so. The easy example is releasing a demon in exchange for a boon.
The "evil" character always has the option of making whichever path is most economical and rewarding. A "good" character is forced to walk the selfless, degrading, difficult and time consuming path that likely isn't going to pan out to be particularly rewarding (and if it is and the PC knows it is, then is it really good or is it just acting selfishly in order to get the larger reward?)
