You can buy a phone with the latest technology in it, designed and built to tomorrow's specification; and AT&T still won't support it, unless the manufacturer has paid them to certify it and put it on this list[0].

Very few people are advocating that they keep 3G around using 5x5MHz of spectrum for little gain; people are just advocating that they not limit consumers from using the supported device of their choice regardless of whether it's on the list.

[0] https://www.att.com/idpassets/images/support/pdf/Devices-Wor...