But it was "good" vs. "evil"
Of course, the question here might be, was it?
That the Excalbians say that the teams are divided along those lines might be sufficient proof to the contrary. Why would they give the game away?
Your reply shows I didn't express my point well, I blame myself, of course.
What i meant by "evil" in quotes that it was in the perception of the Federation characters that people like Kahless and Ghengis Khan are evil. So, the Excalibans wanted to know, "What do mean by evil?"
For example, Lincoln was commander in chief during one of the wars that most of his people died, and he sent many of them to their deaths, as he was in command.
But the Federation people didn't consider him evil.
Ghengis Khan created the largest, stable in his life time, nation in current Earth history there by creating trade routes and causing east west cultural exchange and commerce, and he was considered by them evil.
So, it's not really what
they did, but why similar actions by different people are considered alternately "good" or "evil".
So, back to Kahless. In the minds of most people on the Enterprise, Kahless is like a really horrible entity, "Kahless the Unforgettable, the Klingon who set the pattern for his planet's tyrannies" So everything a Klingon has ever done is "evil" in this point in an over simplified Federation mindset. Being this decietful archtype, I'm not suprised he could change his voice, as it exudes treachery. I'm suprised he didn't have more "powers" but maybe some of the worse things attributed to him were dismissed as legendary, but they belived in his ability to mimic.