I have never, in around four decades of living, had an actual need to determine the mass of a given volume of water, or the volume of a given mass of water.

When cooking, I routinely need to split some quantity of an ingredient into thirds or quarters.

Yet I am also constantly told that I'm ignorant and backwards and irrational for preferring a system that optimizes for the latter, rather than for the former. Base 12 is genuinely better for many real-world applications than base 10, those applications are more common in the lives of non-scientists than the applications metric is optimized for, and I doubt you're going to be able to produce a rational argument otherwise.