Is it considered a major sin for merchants to import glasses that enable the wearer to see what is in front of them naked (even if they are wearing long, loose, non-revealing clothes), and do they bear the burden of every act of fornication that occurs because of them?

It is not permissible to import or sell this technology (spy glasses) because it is impermissible to use them in the first place. Rather, their use is forbidden due to what they cause in terms of transgressing the privacy of others, violating their sanctity, and looking at people's private parts while they are unaware. This is more severe than mere unlawful looking, and it is among the major sins. Importing and trading in such glasses is considered aiding in major sins, which is also a major sin.