Just to precise one thing.
Dark Jedi is not The Lord of the Sith. It's a VERY different things.
Darth Bane trilogy last book (don't quite remember the name) has a quite nice talk about the Dark Jedis.
A Dark Jedi is not jedi serving the Dark Side. A Dark Jedi is so because he didn't accept the rules of conduct and the plain life in the Order. It's a Jedi who serves no one and uses his powers for only one purpose: make his life enjoyable and as long as possible. He would avoid conflicts and escape the Order, and the Order would put him in its "Kill on sight" list, but it won't be its top priority at any time.
He's a bastard, in a word.
Dark Lord of the Sith, on the other hand, is quite a different thing. He embraces the Sith Code and he is subordinate to the Emperor's will. It's as impossible for a sith to be a spy in the Jedi Order as it's impossible the countrary: he'd be noticed after first ten seconds.
Yes, there were cases when a sith tries to forget his past and turns to the Light Side, but it's a different matter.
Turning back to our realities, when you'll be accepted and chosen as a padawan, you will need to learn less than a slice of our history to understand the reason of so negative reaction to this idea.
We had a rich history in these 174 years

Regards,
Elod-hora