Very interesting one, here. Had to think about it for a few minutes - but I'd say a character such as this walks a very fine line between being an anti-hero and an anti-villain (a villain who may be justifiable/sympathetic in his actions or goals, hero-like in his behavior/desires, but the execution of such is so wrong that it is, in and of itself, evil.).
Such a character could easily flip-flop to either side. So in order for such a character to firmly stand on the 'hero' side of the gray-scale, I have to ask - what exactly is holding this sadistic psychopathic character to the side of fighting against evil?
If he enjoys inflicting human pain and suffering, how does he hold himself on superior moral ground compared to the very villains he fights against? And eventually, is it ever explained why he enjoys inflicting unimaginable pain on others, so the audience may better sympathize with and accept such a character as 'good, but troubled/unstable/misunderstood/broken/twisted/f*cked up'? If it's never explained why this character does what he does, and why he is okay with what he does, (and why we, the audience, should be okay with what he does), and it's just tackled as 'normal' or done 'just because', it's an issue.
Everyone is the hero in their own story... So, if the narrative were from just a slightly different perspective, would he be considered a hero at all? Or just a chaotic, unstable, dangerous monster, who justifies his own actions with 'good intentions', whom has too much power, and should be hunted and destroyed like the very villains he fights against?
If our society wouldn't accept such a person as 'good' if the perspective of the story were different, than hopefully the society in the story behaves likewise... (and if you think the society would react differently, simply because death isn't an issue - or would accept it simply because it was a 'bad guy' - just look at how people react to the torture of prisoners of war. No risk of death, and they are 'bad guys', so why the outrage huh? We have the power, so why not? It's not like we're killing them or anything!... catch my drift?)
Or, even if it is to 'reform' the person, would people accept torture as an acceptable means of 'reforming' someones bad behavior? Some people may, but I doubt most people would accept such a practice as good, even if it were for a desirable goal.
As other people have said, if this story and this character is believably & realistically done and well executed, it could be a very interesting story indeed. Choosing to go against the grain of social norms, and the social repercussions of doing such, is usually quite interesting for a story... But if the violence this character inflicts upon others has no negative repercussions, no explanation, and no sympathetic reasoning behind it - it begins to tread into 'mindless violence/gore/torture pr0n' territory.
(TV tropes has some pretty good articles on anti-heros and anti-villains, so, for your reading pleasure: http://tvtropes.org/pmwiki/pmwiki.php/Main/AntiHero
http://tvtropes.org/pmwiki/pmwiki.php/Main/AntiVillain
http://tvtropes.org/pmwiki/pmwiki.php/Main/SociopathicHero
http://tvtropes.org/pmwiki/pmwiki.php/Main/DesignatedHero