I've seen many times people argue as follows: "Energy must be conserved, because otherwise the first law of thermodynamics would be violated." Clearly, such arguing is logically incorrect. The energy conservation law is much more general and fundamental, while the first law of thermodynamics is just a special case of the energy conservation law. What I cannot understand is why such a conceptual mistake is so frequent? How it may appear to somebody that the first law of thermodynamics is more fundamental than the energy conservation law? BTW, have you also noticed people make such a mistake?