That it has not been observed in the wild (which is arguable) does not mean that it is not real. It is quite obvious that a tax rate of 0% would lead to no rev

That it has not been observed in the wild (which is arguable) does not mean that it is not real. It is quite obvious that a tax rate of 0% would lead to no revenue. It is also obvious that a tax rate of 100% would not lead to the full expected revenue, as people would need to evade taxes in order to be able to survive. If we assume that tax revenue is a continuous function of tax rate, there must be an inflection point. The Laffer curve is indeed a curve, but which curve it is is not specified by the theory. The theory simply follows from the argument I have outlied above. It is not a specific curve, it simply states that, if we take tax revenue to be a near-continuous function of tax rate, it must not be a monotonic function, but instead have an inflection point.