What are the advantages to Lightside Sith?

You get to not be chaotic stupid.

Once you've mastered your hatred, you can pretty much keep it in check and only need to utilize it like a finely crafted tool. Not everything is a nail and you're not a hammer.

Finesse certainly exists on the dark side. So yes, the Sith Lord invites you over for tea. Since choking you to death might not be the most effective means to his ends.

Pissing of the darkside people who can't kill people in flashpoints.

This is actually pretty glorious when you win the roll. The rage is palpable.

When I did black talon once I won the light side roll to spare the fat captain dude and the people in my group got all buttmad about it.

That is one way to do it! I only offered some insight as to how one might go about playing a Lightside Sith, or why someone might do so. I did say that said player wouldn't kill unless it benefited them, sounds like killing your master to raise in rank does benefit them.

You don't HAVE to pick all lightside or darkside options. Sure there is equipment that you can get at full darkside and full lightside, but getting maxed out before you hit the level cap is extremely easy. On my smuggler I am all over the place in my choices and still am at Light III.

You can't ruin someone elses alignment as if they are that concerned they should ask before grouping what your alignment is. You choose based on your own responses.

If the group agrees in advance, I suppose that would be different.

coolness factor

You guys think that people get butthurt on sith side when a light side roll wins. Wait til you play a dark side jedi and start winning rolls.

That's not true. I'm cranking a Dark Side Sith Warrior right now and have been crafting/using blue and green crystals no problem...