No, it's really not that simple. Keleth-Ur is still considered a sith lord. (He's the heretic with the hologram in the sith temple on DK.) The sith don't call him the 'jedi Keleth-Ur', they call him the heretic sith lord. They are even aware of the general nature of his heresies, but still recognize him as sith.
As far as the religion analogy, it doesn't hold up. Baptists will tell you they are christians. So will lutherans. As will episcopalians. And so will those small churches full of snake-handlers. Most of these churches still recognize the others as 'christian' (misguided perhaps, but still christian). That's why there are no calls for crusades between these denominations. *wink*
well i do tend to ramble alot
however you seem to have won my argument for me while trying to prove me wrong.
what is a heretic, and more importantly what happened to heretics?
oxford tells us that a heretic is
Definition of heretic
a person believing in or practising religious heresy.
a person holding an opinion at odds with what is generally accepted.
you have to realize that although star wars seems like a much more advanced civilization than our own. in many ways its not. its like something directly out of the dark ages. i'm sure alot of this is because barbarians are much more exciting ppl to write about. spacers fending off pirates, warrior monks, evil cultists, organized crime syndicates as powerful as the ruling governments and the 2 largest super powers in what seems to be a never ending war.
so if we look back to history. what would happen to a heretic? they wouldn't live long. and the lord you are referring to, well hes dead. and i think the reason he is still referred to as a lord, is damage control. to strip him of his title will bring up questions, such as "what did he do wrong" much better to let him and his secret go the grave together and hope no1 ever hears of the truth
as for my religous analogies, you are right in todays world they might not hold up very well. although there is still alot of religious resentment between some faiths, but if again you go back to barbarian times my analogy works fine. if you didn't practice the right kind of religion the right way you were considered a heretic and killed.
in star wars a light side sith would end up in the same place as Keleth-Ur