I am of the opinion that the Force has a will, Celestials, the Ones, the Chosen One etc. all point to this being the case.
However ultimately its irrelevant. Its not so much the Force telling them what to do, but the power promised by the dark side compelling them to desire more and more power for its own sake, in a sense they become 'addicted' to the dark side. Take the Sith of the Order of the Sith Lords. Why were they so hell bent on destroying the Republic and the Jedi? What personal grievances did they hold against them? None. Heck many of the Sith in the Order where just random force sensitives indoctrinated into Sith teachings, then all of a sudden, with no previous contempt for the Republic or the Jedi, or any previous desire to establish authoritarian rule, they attempt to do just that. Why? Because the Republic and the Jedi stand in their way, they block the path to power. Why do the Sith wan't power? Good question, they just do. They have no real goals, they just want more and more power. Traya and Vectivus where they only Sith who broke away from this, they had their own goals, goals uninfluenced by the dark side.
Vectivus was Sith, he used the dark side just as any other Sith did. He was merely not obsessed with conquering the galaxy for no apparent reason, seems the opposite of disturbed to me. And yes, Traya was physically corrupted by the dark side. But that is a result of her 'indoctrination' if you like, to the dark side by the Sith assassins of Malachor V. Who overwhelmed her with Malachor's dark energies. Her corrupted appearance was the result, however after that she made her own path. And rose above her emotions. Vitiate is something of an enigma, he displays the qualities of one who has focused their power, he is cunning and manipulative. And yet he also seems to have become utterly consumed by the dark side, he is so hell bent on achieving absolute power that he is prepared to destroy the entire universe to stop himself from losing it. I'd say he's an entirely different class altogether, 'insane' comes to mind.
In many ways the OP is right, emotions are for the weak. They are the quick path to power, only through meditation and concentration can you overcome your emotions and wield the dark side to its full potential.
I always got the impression it was (from a film stand point) that giving into one's emotions was giving into the dark side in so much as it was the road of easiest travel. Easier to obtain the power you want by going DS than obtaining the power you want and being LS.
One says more training, the other says, don't have time, need it all now!
They say give into your emotions, your passion, and love for others can be both of those.