I would argue that being limited to a single unit system is like being limited to a single language. In principle, no one needs more than one but in practice the differences in expressiveness for different purposes are interesting and useful. These differences in expressiveness are connected to the continued existence of different systems.
America is big enough and is sufficiently independent of trade in its economy (most of its stupendous production is also internally consumed) that the cost of not transitioning to metric is marginal. I understand why metric is a good system but simultaneously understand why the benefit of metric is dubious for the average American. Remember, American units are defined in terms of metric units; it is a preference, an American can precisely convert to metric at any time if they deem it useful. But they don't because it serves little purpose.
Basically, like their language, Americans occupy a big enough economic sphere that they get to define their standards. An enormous number of global standards are American in origin as it is. I don't sweat the lack of metric even though I use it routinely. Once you become familiar with enough unit and arithmetic systems, you quickly learn that they all suck in some context.
It is pointless to turn these things into religions.