If it’s the best strategy: sure. That’s exceedingly rare, though: usually you don’t stand a chance in hell. Still, if it’s the best argument you have? go ahead.
Again: adversarial system. it’s a bloody court room, not a legislative assembly.
Also as to your second point: sure, those can be out of sync. that’s a *perfectly* reasonable situation; to argue that they never affect each other though, is bullshit. therefore, it’s worth a shot. doesn’t have to influence, but it *could*. that’s all you need.
And the distinction you’re trying to make off the bat is entirely nonsensical. Arguing that the law is not altogether on point is potentially a part of a vigorous defence. Fuck, your supreme courts would be out of the business of criminal law for a large part if that was not part of a vigorous defence. And yes, I fully agree going after, say, the death penalty for mentally retarded defendants is a hell of a more noble cause than this; still, it is offensive to make that distinction in whether an attorney should be able to argue, rather than in whether his point should be given any merit in a judgment (which is where the smackdown to this bullshit rightfully belongs).