Any law will, at some point at least, become to vague. On the other hand, I too have the perception that bills are often carelessly written and too vague[0], but I think your understanding of jurisprudence or what a judge's job should be is not realistic. The system is not meant to be mechanical.

I think that for meaningful discussion to be possible, you would have to provide a much more specific, concrete example; but that of course runs the risk of being beyond the understanding of us non-lawyers.

[0] Somebody on HN opined that this is because most politicians are lawyers, and they have an interest in preserving/increasing job opportunities for lawyers, or something like that. I wish I could find the comment.