Dark Side Character, Light Side Companion
Going Dark Side in Star Wars: the Old Republic is a double-edged sword (or possibly a double-bladed lightsaber?). On the one hand, it's fast, fun and furious. Conversations tend to take darkly-amusing twists, conflicts are resolved quicker and usually more violently, and you get to live out revenge fantasies in a harmless way. On the other hand, nobody really likes greedy, violent psychopaths. Some may obey the greedy, violent psychopath out of fear, or possibly out of respect for his power, but nobody really enjoys his company.
This goes for your ship's crew as much as for anyone else. Companion characters have joined your cause, but the way you go about achieving your goals may not sit too well with some of them. Especially if you are going full-on Dark Side and your companions are more attuned to the Light.
If full-on Dark Side is your goal, check out Dark Side Character, Light Side Companion for tips on how to keep your soft-hearted shipmates from hating your evil, black guts.