A very small part of the country is connected by fiber, and fiber connections are always symmetrical. The vast majority of consumers still get internet via coax cables, and bandwidth is very much an issue on those.

No, a very small part of the last mile is connected by fiber. Trunking is always fiber these days. As are local neighbourhood branch points, if your provider evolved from a telephone company. (If you live in an apartment building served by an ex-telephone ISP, you likely have fiber run all the way to the network closet of your building, with only the per-subscriber in-wall wiring switching over to copper.)

ISPs that evolved from cable companies might still be using cable hubs with a common collision domain, but only a relatively small number of subscribers will be riding the same copper — it’s just cheaper these days to convert the signal to fiber as early in the signal path as possible. Plastic wires are cheaper than metal wires, and you need fewer of them (and so fewer switches.)

Yes, *fiber* can. But the majority of Americans use Cable/HFC (DOCSIS) technologies. These were designed as a one-to-many closed loop TV broadcast on a coax line. Except with the incoming DOCSIS 4.0 deployments it's always been asymmetric as a limitation of the technology

Fiber is not ubiquitous. Many of us are still on DOCSIS over copper, in which case the person you are replying to is exactly correct: upload speed can be reduced for additional download speed.

True FTTH is naturally symmetric; PON is not nor is Cable.

No, I think you might be confused. We all know that the fiber for the download link is at least 10x wider than the fiber for the upload channel. There's just no way to squeeze the same number of bits through the smaller "tube" /s

Though the fiber system as a whole may not be capable of symmetry. For example GPON with 2.5gbps/1.25gbps up/down and 10G-PON at 10/2.5 up/down.