What do you mean "start as evil?" Do you mean that you start leaning towards the evil side of the spectrum? Or do you start with the ability to research concepts of malice (as though you had researched xeno ethics). If you start as a formally declared evil civilization (able to build evil bonus structures, research concepts of malice, etc.) then I guess something's funky with the game files. BUT... if you mean that you start leaning towards the good side of the spectrum, it's pretty easy to explain. Some civs (like Altarians) start the game leaning towards one side of the ethical spectrum. But that can be altered either accidentally or deliberately. Furthermore, custom civs can easily start while leaning towards one side or the other. Although you can't modify a custom civ's ethical start point while creating the civ, once it is created you can add your custom civ as an opponent and then choose to "edit" the opponent. While editing the custom civ as an opponent you can adjust ethical alignment. Then simply save the custom civ, click back to the screen where you choose your own race, load up the custom race, and you should now start with a non-neutral ethical alignment.
In short, it may be a glitch -- or you may have simply modified the starting alignment (whether on purpose or accidentally).
