Okay, so...a Jedi is a Light Side affiliated being and a Sith is just the opposite. Why is there so much fething crossover here? Yes, Revan used both and so did Luke, but they were special cases in which plots were written around. Revan himself only was an exception due to having his brain wiped.

Other than a need to feel special and/or be overpowered, why would a typical Sith use Light Side skills or vice versa? I am not talking about Force Jumps and other universal stuff. I'm talking Force Lightning, a very Dark ability and something like say, Battle Meditation, a very Light ability. The fact that Plo Koon and Luke used it is crap, imo, but whatever. 'Electric Judgement' is a bullpoodoo way of writing around the fact that Lightning is learned through experiencing it and will thus be always tainted with pain and rage.

Or a Jedi using Juyo without turning Dark. It's well established to be a bad, bad idea for Jedi to use it, especially ones with anger issues. Sora Bulq, Depa Bilaba they both went evil from it and even the mighty exception to every rule (Anakin) was specifically not allowed to learn for many of those reasons. But Vapaad, you say. Bull. Again, those who attempted to learn it went psycho except Mace Windu for some strange reason.

Strange, because Kas'im called Juyo by the V word 1,000 years or more before Mace did. So, Mace was using Juyo but had formidable mental strength. That isn't a trait every Force user on the Light Side shares to that degree. Even Yoda avoided it and was leery of Juyo. Hell, Sidious called it a 'Sith' style which is a pretty strong endorsement when the Galaxy's most evil bastard calls it such.

A Jedi shouldn't be learning Dark Side skills because they have a strong tendendy to corrupt. Exar Kun, Set Harth, Anakin and lots more dabbled and eventually fell. A Sith shouldn't have Light Side skills because the very nature of the Dark is so different as to make using Light Side abilities nearly impossible. Not to mention a Sith would scoff at the notion of lowering themselves to doing it. They believe in the power of the Dark Side so strongly as to not even consider alternatives.

I can dig the idea of a Grey Jedi who follows their own beliefs, but that's a belief system. You follow you, not a proscribed Code. However, if you start as a Jedi then a Grey but dabble in the Dark Side...you are a Dark Jedi or even a Sith. Again, for the reason it corrupts. You could redeem yourself as redemption is well established but that means the Dark abilities become a no-no.

One of my favorite canon characters is Qui-Gon, a famous example of a Grey. He defied the Council but never touched the Dark Side. He may even have risked being kicked out if he didn't serve the good in his actions (plus he had a sweet beard, a good reason to keep anyone around).

You might argue 'I can do what I want', and you could. I'm just saying these indistinct lines don't make sense even in a fanon context.