This is misleading. Adam Smith presented this as a possible solution to an economic paradox at the time. But later philosophers came up with much better solutions:
https://en.wikipedia.org/wiki/Paradox_of_value
There's no reason to believe that Smith wouldn't have latched onto the much better solution. So being hell-bent on the incomplete answer from the 1700s is a unique peculiarity of Marxist theory.
> But later philosophers came up with much better solutions
Yes, later than both Smith and Marx. Marginalism didn't go mainstream until the 1890s, though the necessary pieces were there waiting to be assembled from about 1870.
fair enough. Maybe my dismissal was too shallow
The labor theory of value was accepted wisdom prior to the late 19th century: it originates with Adam Smith and David Ricardo. It's wrong (or more accurately, not a good conceptual framework) but it's not obviously wrong, let alone "idiotic".