You ought to distinguish 'the law' that can be discriminatory, unjust, imperfect, and 'the rule of the law', which in theory cannot. In practice, the 'rule of the law' was never truly achieved, nowhere, and recently (post 9/11 it seems) the US might have gotten further from the hypothetical 'perfect state'. Presidential pardon, Guantanamo, or I think closer to everyday life civil forfeiture, or arrest without cause, interrogation without a lawyer...

Some exceptions to the rule of law are just good practice: immunity to the executive power from executing a voted law, immunity for the legislative power (in some countries like France this immunity have some caveats) while elected. Sadly it breeds corruption.