Sort of like everyone else, my gut reaction is "Of course not!"
My next thought is "murder is murder", and furthermore, how do we know the victim is a gangbanger for sure anyway? Or that the next victim might not be a little girl caught in the cross fire? And besides, the victim had a family too, and they deserve to have their loved one's killer brought to justice, even if their loved one was nothing to brag about himself.
But my next thought after that is that gangbangers generally kill for a reason, and the people they kill are often (though not always) themselves caught up in crime. It might be a rotten drug deal, or a revenge killing, or a fight between gangs . . .but the victim likely played some role in leading up to his death, and the motive of the killer, however inadequate to justify murder, is likely comprehensible.
People who intentionally kill children, however . . . not only do most people not understand their motives, but their victims are pretty much by definition innocent. And they often kill again.
So . . . yeah, in a world of limited resources, more effort should be expended figuring out who killed the kid than who killed the gangbanger. 1) because the child-murderer is probably more dangerous (at least to innocent people minding their own business) and 2) because the victim in that situation likely did nothing to provoke or bring out his own death.