By definition, if a law is unjust, then following it is immoral (that's all it can mean for a law to be unjust) and thus disobeying it is not just morally licit, but morally required.
But that's missing the real issue. It's all well and good to talk of a hypothetical, theoretical "unjust law", but this premise assumes perfect moral knowledge on the part of the individual. Real individuals, of course, fall short of that. Moral error is a universal fact of human nature, I'm sure even atheists concede as much. So the real question isn't "is it right to break an unjust law?" but "is it right to break a law that I (possibly mistakenly) feel is unjust?"
There are many factors to consider in answering that question, of course. The most important is who made that law. If you live in a democracy, then the presumption is that a majority of the citizenry believed the law to be just (obviously the gap between the ideal democracy and the very flawed reality we see is quite big, but that's a question for another day). And if a majority believed so, then I'd say that in almost all circumstances the right thing to do is to defer to one's peers. Who the hell are you to say the majority is wrong? Of course there are exceptions, but they are rare and should be fully motivated.
I find your arguments very lame. If you believe in your bones that obeying a law is unconscionable, majority support for it is no reason to obey it. There are numerous examples of majority opinion being wrong. You're essentially saying that people should forfeit their individual consciences--a very dangerous and scary proposition. Should civil rights demonstrators in the South have deferred to the will of the apparently pro-segregation majority? By your logic, "who they hell" were they to object to segregation? Should Underground Railroad workers before the Civil War have likewise deferred to pro-slavery public opinion?
And if those contemplating breaking a law lack "perfect moral knowledge," don't those who made the law lack it as well? Your point here cuts both ways.
Additionally, you overlook the fact that even if a law is considered generally just by most people, there may be important exceptional situations where it is not. When most people think of laws against murder, they're not imagining someone putting a loved one out of their misery at the person's own request. Legally that is murder, but it's not what most people have in mind when they hear the word "murder," and it's not at all clear that most would think it would be wrong for someone in that situation to disobey the law.
