So IMO having an evil alignment does not make anyone evil. Instead DM can choose whether anyone has "aura of evil" case-by-case basis. Like for intance committing yourself to pure evil, such a belonging to an evil cult could make you evil. Also thinking evil things while the spell is in effect could make you evil at that moment (even though you're neutral).Alignment is a tool for developing your character’s identity. It is not a straitjacket for restricting your character. Each alignment represents a broad range of personality types or personal philosophies, so two characters of the same alignment can still be quite different from each other. In addition, few people are completely consistent
I'm playing a paladin in Pathfinder and that's how my GM has made it work. If I decide to use Detect Evil actively, it's like the spell, but I also have a general "evil-sense" as you describe. It's very effective, especially since I'm the only player and so the campaign is focused on my character. I can see it being less useful/effective/desirable if there are multiple PCs with different goals, motivations, classes, and alignments.In addition, it worked nicely giving the paladins an always on "hairs pricking on the back of the neck" power. When they came within 30ft of supernatural evil they knew it was present, but it wasn't a directional power IMC.
But isn't the point that in this game, alignment isn't that subjective?Besides, alignment is too subjective. A person that the majority in society deems to be evil, could be good in their own mind. Even the sickest of actions can sometimes be justified.
However it is a requirement for typical paladins to "punish those who harm or threaten innocents."Furthermore, one doesn't have to kill someone just because they are evil, though there may well be hardliners who do take this exact approach. It's not uncommon for paladins to be played this way, however I don't think it's the only way a paladin can be played.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.