I'm pretty liberal, so if you'd like to qualify these militia groups as "conservatives" then have at it. I throw them into a different grouping though. Simple nuts.
Anyway, of course the outcry when whites are...."discriminated" against(though I would object to that classification, lets go with it). Whites are the majority. This isn't some little secret that needs to get exposed. Not to mention you're not going to have white people discriminated against in any other general walk of life as a result. So they're a safe group to use in this setting.
Plus, it IS a real threat. It's not like they just defaulted to them because they're a 'safe' group. Sure, that was likely part of the equation, but the real and present danger was likely the driving force.
Anyway, not sure of the exact definition of "terrorism," but I assume it's something along the lines of an attack on civilians and or Gov't officials meant to create fear and motivate political(or religious) changes.
I think Gang wars are just meant to scare rival gangs off, or....whatever reasons street gangs would have. The Cartel system would operate in much the same way, to protect their trade.