In the abstract that is certainly true, but you are missing the bigger picture. You are acting as though people are somehow able to discern what is and isn’t an emergency and decide that all by themselves with perfect accuracy.

The point here is that it is preferable to sometimes use resources badly in order to avoid sometimes not at all using the resource when it would be necessary. The point is to not discourage people from calling 911 (or the local equivalent).

If there actually are constrained resources† then, sure, that cultural value should probably be set somewhat differently, but I cannot for the life of me imagine why that should be the case in the US. It’s not necessary to set that value differently. (If it were that would be a real shame for US healthcare and you should demand immediate change from your political representatives.)

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† I am aware that at some point all resources are constrained. What I’m talking about here is that the system should be designed in such a way that there is spare capacity availible at all times when looking at the maximum number of required ambulances at the same time during, say, the past twelve months.