Coinbase's opinion on the matter is pretty irrelevant to determining what is and isn't a security. The fact that they tried to get the SEC to tell them what they were doing was or wasn't allowed (never mind the fact the SEC likely had an ongoing investigation that prevented them from commenting in the first place) is wholly irrelevant to the fact they were actively breaking the law.

At your behest, I did go to the footnotes. And my read of the footnotes is not that they're an extensive citation of case law to justify their points. (There's just 5 cases cited). Most of the footnotes are citations to various other exhortations that essentially amount to "we think existing financial regulations are too onerous for cryptocurrency companies, please loosen them." Again, there's very little "we think the regulations are unclear," but rather a lot of "we can't do what we want to do under these regulations, please loosen them."