> It's a mechanism to show that there is a certain floor on value of an economic good, which is raised every time constructive labor is applied to a product.
The problem is that this argument is circular: whether the labor is "constructive" gets judged by whether it succeeded in adding value.
Equating Marxism to labor theory of value is akin to maybe equating economics to a supply/demand curve.
There are unequivocally true parts of Marxism, such as surplus value of labor, and the fundamental incentive conflict between a capital owner and laborer (which Marx deems exploitation)
The labor theory of value is also I think misinterpreted by modern economists as a price-setting mechanism, which it isn't. It's a mechanism to show that there is a certain floor on value of an economic good, which is raised every time constructive labor is applied to a product.