I have a big problem with keep a law vague and having people interpret it as they see fit, in accordance with the spirit of the law. This is dangerous as it allows for arbitrary, inconsistent interpretations which do little to ensure justice. Having a vaguely written law makes it hard to ensure the Rule of Law is enforced.
People are sometimes tempted to advocate a spirit of the law approach over a letter of the law approach because they think this can help to avoid loopholes in the law. This is true, technicalities cannot be exploited if the wording is not precise enough to allow for technicalities. However the potential cost of having the law open to interpretation outweighs the real benefits of having a precisely worded law.
Whatever the spirit of the law may be, it should be possible to articulate that as precisely as possible into clear and concise written law. Things may be missed and people may find ways to violate the spirit of the law, however this is when the law is revised and any such loopholes fixed to prevent the problem from occurring again in the future. Letting a few people get away with doing something reprehensible should be much preferred to allowing inconsistent interpretations of the law to be doled out and for justice to be doled out subjectively, based on the person doing the interpreting.
Allowing for a lot of interpretation so the spirit of the law is considered more important is nice in theory but it all it really accomplishes is ignoring the Rule of Law, denying justice to people and enabling mob rule. Juries will be free to find guilty those they dislike and let go those they do regardless of if the law was broken or not. Sticking to the letter of the law removes personal biases and should only allow for interpretation to the minimum required extent. It seems like this should be basic to anyone who has thought it out. Yet people still advocate vaguely written laws and adherence to the spirit of the law, without seemingly bothering to consider the consequences.