It would be a lot more worth it if they'd imported the KotOR II or DA2 system instead. As it stands now, disapproval is absolutely negative period. You never want it, it's actively detrimental to anything you could ever possibly do. It hurts your crafting, it prevents you from picking up the +10 presence perks, and, most importantly, it chokes roleplaying. Piss off a companion and you don't get to talk to them. This is the absolute opposite of good game design; it punishes you for playing a relationship in-character by removing the ability to continue to explore that relationship.
If conversations unlocked at negative approval intervals as they do in KotOR II or DA2, perhaps even with a few lines changed here and there to reflect the difference in affection vs antagonistic respect, it would be a much richer system, and I wouldn't have completely abandoned any sense of immersion or RP honesty by repeatedly selecting douchebaggy lines on Belsavis and Ilum dalies just to get Scourge to talk to me or have to choose between Elara being a mute puppet for fifty levels or else inexplicably adoring my verbally abusive darkside Trooper as an exemplar of the Republic and loyal friend because I smothered her in gifts.
Agreed, a viable positive/negative influence path would be interesting and rewarding.
On the other hand, some of these companion recruitments are forced enough already; shoving Ashara onto my ship and then giving me a maximum antagonism meter would just be miserable. With the current one-directional scale, at least one of us (i.e. her) thinks that we have some kind of relationship/reason to stick around by the end of the conversation line. DA2 suffered badly from this effect: I loved its affection/rivalry scale but hated that there was no reason whatsoever for most companions to not just stab you in the face and walk away at max rivalry.
There are ways around this: In a world-saving scenario you can justify either positive or "I hate you but we have to work together" companion relationships, and I would love to see both developed as viable paths. Likewise if there's blackmail/usefulness. Doctor Lokin is with me because he blackmailed his way onto the ship for his own reasons; in-character I hate that he's there but out of character I love, love, love that they wrote it. It makes it make sense for him to stay even though my character dislikes him.
As it is I'm reduced to RPing the hell out of conversations because that's what I want my character to do, then pumping companion gifts to cancel the fact that by any rational measure my companions should hate me. Don't get me wrong, it's good that the gifts are there from a mechanics perspective, but it is there in part to compensate for the disappointing fact that there is only one conversation line.