You can game the thing so that you can still get light side mastery without being a complete liberal. You can even do all of the assassination quests for the Rodian on Manaan if you want. The trick is to front load your bad actions in the game and then redeem yourself later. It seems that you get penalized for darkside actions more if you have a high lightside score at the time. There are enough lightside points on Korriban alone that you should more than be able to make up for some darkside moments (there are more opportunities for lightside points in the game than you need for mastery). And interestingly, you can do some pretty morally ambiguous things and not get penalized for it (especially on Korriban), but I won't spoil it.
Also, realize that you can easily finish the game without mastering either light or dark, so you can play neutral if you want without making anything hard on yourself. The ending isn't even determined by your lightside/darkside score anyway, but is determined solely by your Big Decision on the Unkown World.
Cool, I'll keep it in mind the next time I replay. Though I didn't mind giving the credits to the bounty-hunted dude on Taris, raising a mental middle finger in the direction of Ayn Rand the whole time. ;-)
Meanwhile, I'm thoroughly engrossed in Thief: Deadly Shadows...I've only been waiting for that game for three years, after all. So my Bioware stuff has fallen by the wayside for a bit.