It is pretty weird for a PC. That's why it's a flaw. It's also a nice RP mechanic.

And in less Grim and Gritty games (such as ones involving, say, Flamingly Gay Trolls) it might fit in just fine.
But it's easy enough to add to a character.
Maybe they run the shadows because they truly believe the corps are causing the death of the human spirit, and they want to bring them down to let humanity truly be free. They distrust all corps, but believe their fellow Man can do no wrong.
Maybe they only take jobs they feel to be "right" and not criminal.
Maybe they simply don't understand what it is they're doing - they could be somewhat touched, and simply be unable to make the connection between their actions and the negative results. THey might see it all as a game, and be genuinely puzzled if you tried to explain to them that the people won't get up after you leave.
Maybe they're self-deluding. Their parents lied and betrayed them, and ever since, they have brightly assumed that everyone is on the up and up, because dammit, they need the world to be that way.
I do agree that it has a nice potential to cause a snap that results in a replacement negative quality fairly easily, though. Which would be a nice session.
But I've known people that fit this category that were involved in traditionally cynical businesses, so it does happen.