Cliche as it is, "all is fair in love and war" is actually a legitimate reason–as far as Guild Wars 2 community manager Ramon Domke is concerned. In response to a thread complaining about "night-capping" in Guild Wars 2, he had the following to say:
Hi Everyone,
All is fair in love and war – and as love, WvW is a battlefield.
There are exploits, I’ll give you that – but then there is coordinated effort to ensure your world or your team uses each and every resource they have to their advantage.War is not fair, war is not pretty, war gets out the worst in us – and the best – and even if we have excluded open world pvp from the rest of the game, this is exactly what happens on the WvW maps: It is the ‘playground’ for strategists and great tacticians, it is the place for coordinated efforts and mean ideas in the middle of the night.
Night capping is one of those valid tactics to score some points in a lasting battle – to get your world the upper hand, or cancel out daytime supremacy by another well coordinated opponent.
As Guild Wars 2 will progress in time, so will world vs. world and core gameplay mechanics. But for now, night capping is one valid possibility to ruin your enemie’s days – pun intended.
For those that don't know, the issue that people are complaining about is that dominating in world vs world can grant your server large PvE bonuses. In WvW, you're battling against two other servers–except that sometimes, the time zones don't synch up, or people can launch attacks when everyone else is asleep. So Ramon is implying that these are legitimate tactics, even though people feel they can't really do something about it.
Ultimately, whether he's wrong or right…the fact remains that you can do it in the game. So long as that's true, it doesn't matter what people think. It's possible to do, so people will do it.