> >"Conflict of interest" in lawmaking is a concept which only applies to people to whom additional authority beyond that of citizen of granted to act as an agent of other citizens
> That's precisely what a voter is doing.
No, its not. A voter is voting on their own behalf as a citizen, and not graned additional authority beyond that of a citizen to act as an agent of other citizens.
> According to the Constitution, the citizen is sovereign.
One might, perhaps, argue "according to the philosophy to which some subset of the framers subscribed, and which motivated the Constitution, the citizen is sovereign", however, to argue as you do is absolutely without support; the Constitution does not mention sovereignty, and insofar as it expressly grants the traits associated with sovereignty to any entity, it does so to both the states and the federal government, but not anyone else.
> Therefore, when one votes, one is acting in a purely public capacity, completely separate from one's private interests as citizen.
Even if one accepted the preceding claim, this doesn't follow from it. Individual sovereigns (as opposed to sovereign republics) have no distinction between private and public interests; that's the key thing that distinguishes a Republic from a Monarchy, that in the former government is not a private function. So, the idea that Constitutional sovereign citizenship (if it existed in the first place) would imply that citizens had both "public" and "private" capacities that were distinct is completely incoherent -- if individuals are sovereign, their public sovereign capacity is exactly their private capacity.
> Even Congress recognizes this about itself
Congress is, rather obviously, a body of people who each exercise additional authority in government beyond that of a citizen-voter representing themselves, and who are instead empowered to act as agents representing the interests of other citizens. That's the whole point of Congress.
> it passed Amendment 27
No, Congress doesn't pass amendments. Congress proposes Amendments (Amendment 27 was one of the 12 initial amendments proposed as the bill of rights.)