I think there are a few different ways a person could be neutral. But I also think that by far the most common is people who believe that they're good, and think of themselves as good, and even try and do good things fairly often...
...just not quite often enough. People are really good at being selfish. And really good at lying to themselves. And really good at persuading themselves that this selfish thing they're doing is totally not selfish and totally something they're doing for the sake of someone else.
Of course, they're not thieves... but they will help themselves to a bottle of booze that's sat around unattended. After all, someone's lost it. Or they wouldn't steal from anyone who couldn't afford it... but this time? This one time? This specific person clearly can afford it, so it's okay! And never mind that that happens every fortnight. And they'd never f$$* up a friends relationship! But it was obvious that that last partner was a bad idea, so they were just helping the friend see it. Or they're not corrupt, but everyone knows that some free drinks now and again is just a perk of the job. Or they're not cruel, not sadistic! But sometimes they're in a bad mood, and they lash out, and it's not their fault because they'd had a few drinks and everyone knows what they're like after a few drinks.
So I think for most people the path of neutrality is the path of making excuses for your own petty selfishness, but keeping your selfishness petty enough that you can still excuse it.
I would add that one of their justifications for being selfish or petty is, "I am been a good boy lately, I can't be nice all the time." They do good, but like the bad things it is a lot of little things that don't really add up to much.