I don't think I'd rely on that if your life or freedom are at stake.
Unless there's a mind-reader in the courtroom... I don't think someone is going to be able to get inside a person's mind and see how that person made their determination ... :-) And if I think a law is unjust and should not be enforced, then I'll vote not to convict someone on the basis of that unjust law. And there's not anything that anyone can do about that (and that's one of the "beauties" about" knowing stuff" before you go into a situation like that).
What you know in your head "stays in your head" doncha know... :-)
If you refuse to deliberate, though, and one or more of the other jurors report you to the judge, you may be subject to some close questioning and find yourself in contempt.
We've had a run of cases here recently where jurors were removed from cases for refusal to deliberate. They fall both ways -- in some cases it was decided that it wasn't actually a refusal to deliberate but a decision on the facts (not the law) and the conviction was reversed. In others the removal was held proper. In either case, the appeals court mandates inquiry of the juror, under oath.
But if every juror decides simply not to enforce "unjust" laws, and every juror has his own ideas as to what's "unjust", what kind of mess are we going to be in?
I don't think you've thought this through to its logical conclusion. If laws can't be relied upon to be enforced by the legal system (i.e. the jurors) then it's going to be chaos.
There is PLENTY of room for you to acquit almost any defendant either in finding facts or applying the law as charged to the facts, without going to this extreme a theory. The concept of 'jury nullification' as you propose it means that you will be lying when you take your jury oath, you will set yourself up as the sole legislator and judge as well as jury, and you'll violate the whole concept of the English system.
Other than that, I guess it's o.k.