There is no shame in having shadows, we all have them to varying degrees. To judge darkness as bad or wrong is akin to judging whether up is better than down, or whether blue is better than red.
Myst was an assassin working for a shady government agency, that is until she ended up as a pony in Equestria. Soon after arriving she is forced into the Isri Conflict. Through this experience she learns about herself and questions what is right.