There are people who suggest that a DDoS is just a 'digital sit in', a legitimate way for someone to air a grievance, if they think the targets (or world) haven't paid them enough attention.
This view makes DDoS seem more normal or even romantic/heroic, and spreads the tools/know-how more widely. So, pulling off a DDoS becomes a more plausible and attractive aspiration, for a larger set of surly people with marginal reasoning skills and destructive impulses.
The DDoS tactic should be rejected as dishonorable censorship and vandalism, no matter the cause under which it is launched.
The primary association most Americans have with sit ins is the civil rights movement, but it seems likely that almost all cases where someone refuses to leave an establishment after being asked to leave by the manager the person is being an asshole, exactly like the average DDoS'er.
The default assumption when you see someone unwilling to leave a bar is not that they are noble, and neither should it be the default assumption for a DDoS. That said, I don't think it is reasonable to say no DDoS could ever be noble, just that the vast majority of the time it is just someone being an asshole.
Should anyone care? Once someone launches a DDoS, their argument is invalid. And reporting the grievance might just encourage them.
I don't know anything about any of Github's attackers, but from other incidents I know of at other services, it could be anything. A billing dispute. Anger that something was taken down... or not taken down in response to an unreasonable request. Anger that an account was suspended... or that some feud-rival's account wasn't suspended. People throwing "do it my way or I'll take your site down" tantrums may not make sense to anyone other them themselves.
This view makes DDoS seem more normal or even romantic/heroic, and spreads the tools/know-how more widely. So, pulling off a DDoS becomes a more plausible and attractive aspiration, for a larger set of surly people with marginal reasoning skills and destructive impulses.
The DDoS tactic should be rejected as dishonorable censorship and vandalism, no matter the cause under which it is launched.