You're missing two critical points in the regulations. Here they are: Point #1: Amateurs are allowed to homebrew and modify radios for use on the amateur bands - and ONLY for use on the amateur bands. Such homebrew and modified radios MUST meet certain standards of transmitted signal quality. IOW, being homebrew or modified does NOT give hams a blank check to build or modify radios that transmit low-quality signals. Point #2: Manufacturers who SELL NEW radios have to have them pass FCC certification. The radios have to meet certain standards in order to be FCC certified. There you go.