I don't believe anyone has said it is. We've complained that 1) the Infernal Warlocks are evil, and 2) there's no obviously Good choice. Both of those are consistent with "Feral/Shadowy exist, and they're creepy.
Just to be clear, I'm cool with creepy as a choice. I just want Good to be a choice too. Preferably even more than one "kind" of Good. You know, like Clerics.
The difference is that Warlocks get their powers from outsiders. That says a lot about the alignemnt (big-A or little-a) of the person who asks for/gets/uses those powers.
Fighters, wizard and rogues don't have to work with angels to be good because they don't work with any outsiders at all for their daily powers. They can just be good, evil, or any point in between however they choose. But a class that gets its powers from outsiders doesn't have quite the same flexibility.
Now, Wotc_Logan brought up the point that Warlocks could somehow be "stealing" the powers of Devils, and using it for good ends. If the Warlock is truly independent of their power-source's desires, that changes a lot. Both the flavor (which has been badly misrepresented) and the Alignment consequences.
Though personally I'm STILL disappointed there's no "Elemental" Warlock who gets his powers from dealing with Djinn, Efreet and Dao. And I'd also like to see a Angelic/Super-Eladrin Warlock. Personally to think of an "mostly good" Warlock "I do good, but on my own terms. You helping or not?"