Parent's point is that your Oregonian congressman is not looking out for your interests but those of his resident-constituents. If emigrants comprise a population roughly equivalent to Maryland, why don't they get their own representation?
In France we have I think 10 or 12 seats in the House and roughly the same in the Senate representing 5 regions of the world. You register and vote in your embassy or consulate. So expats do have representative looking for them and their specific needs. And it seems fair to me. And as far as I know, expats don't pay french taxes. So clearly a pretty different focus on that matter.
Apparently even in the US the Democratic National Convention gives state-level recognition to Democrats Abroad, an organization for overseas Democrat voters.
His point was "taxation without representation", which is false. Your point is more nuanced and interesting, I think. I suspect it'd take changes to the constitution to enact, so is likely not feasible, unfortunately.
