truth be told, I never was a big DCU fan, I find Superman Boring, the Green Lantren to powerfull and the Flash and the whole 'fastest man alive' thing a bit to much in the sens that they don't leave their enemies a chance, which is whay DC turned to the idea of Bizzaro, Revers Flash and Sinectro and the yellow ring.
but Batman is a different story, he's human, whith no superpowers or magic rings, just skills and wit. and then came Robin and spoiled everything. I don't mean the new, Dark and fully grown Robin, I mean the Original, speedo clad, Boy Wonder.
so in that aspect, Nightwing is the remedy for that. Batman wouldn't kill, that's his 'one rule' and as Robin, Batman's sidekick, you have to follow that rule, But Nightwing is an EX-sidekick, so as a criminal, I'm thinking "Batman will Brake my bones but won't kill me, so I guess that's fine, Robin is just a boy and he does whatever the Bat tells him to do, But Nightwing is a former Robin, he was trained by Batman and then they had a fallout, so he's to extreme for a guy who beat the crap out of criminals nightly, I don't want to mess with this guy"