To be sure, there's a good discussion to be had about this, whether it should be the parliament or the judiciary that can rule over this, or both, and different countries have different balances in this area.

Generally speaking however, the law and especially the constitution is full of abstract and fuzzy concepts, and judges have ample experience in adjudicating those, as well as balancing them against each other. And don't come to me with alt-right reasoning about what is accurate, true or false. Basic truth isn't too hard to determine.

The main thing is that there should be checks and balances, especially on the executive branch, and currently the US is dismantling them in bulk.