well lets look at a fact
when there is a sith force ghost they are bound to the madder world by there rage and are forced to stay at there tombs and (as seen many times) they can "killed" for lack of a better word. however this is because of there power. as in the end of ROTJ we see anikan because he was very powerful and of coares he turned away for the dark. almost all sith lords turn into force ghosts as we have seen. now qui-gon was able to do so and he told yoda and yoda in turn told obi-wan. the jedi way is forged by peace and power in the force at the same time this is why even after qui-gon died he contacted yoda to perpar him because he was (even thought he made the method) haveing touble with it. this is proven because obi-wan who had 19 to perpar at first could not come before luke (it toke him three years) wile yoda did it very soon after his death because he was more advanced. now anikan did this due to his power gained though the dark side but if he didnt trun to the light his spirtal from would suffer the weakness all the other sith spirts do. but he turned to the light adding peace to himself plus thepower let him do it automaticaly.
so what im geting at is the sith path and jedi path are both needed to become strong because one with out the other slows one potencal