You seem to be downplaying the actual influence of the Dark Side on one's mind, as far as the lore goes. One can contain it, but can't fully control it without fully succumbing to it. Those who give in gain its full power. Those who don't either turn away from it, are destroyed by it, or become gradually more and more corrupt. Passion fuels the Dark Side and practising it regularly strengthens its grip on one's mind.
To avoid digging in the literature, take Yuthura Ban from KotOR, for example. Ex-slave, Force-sensitive, became Sith to gain power to free her kin, to destroy slavery. Instead, she found herself becoming the oppressor, caring less and less about those she swore to free and more about power and influence.
If you're playing a "light-side" Inquisitor, then he should adopt a measure of peace and contemplation, rising above passions to control his consciousness.
My suggestion is - if you want to play a "good" Dark-sider, you may want to either make him a little more Jedi-like (instead of slapping an amalgam of surface qualities of "good" person"), or make him darker.
Example - my Warrior, Lord Veridictus, I played as a "Sith Samurai". Devoted to his Emperor, loyal to his people, fair to the men he commands. He has honour, he has integrity, he has persistence, he has patience. But this does not make him any less of a Sith. He relishes in bloodshed, surrendering his mind to the sheer fury of the Dark Side and becoming one with it. He takes pleasure in disarming his enemies and crippling or killing them with his bare hands.
The Dark Side weighs heavily on his mind, regularly sending him visions of brutality and slaughter. Visions of him breaking, maiming, killing. Visions of martial and Force techniques that he's never seen before and that he was willing to try out. The Dark Side rewarded his dedication by unveiling to him new ways of violence.
Now, he is balancing between leaving behind all that holds him back - his loyalty, his honor, his dedication, and turning away from the Dark Side which is close to overtaking his mind, destroying the last bits of who he was.
Nice post, gave me a lot of ideas.