Why are we worried about BANK being deemed a security? Essentially because under many jurisdictions the issuance of a security is highly regulated and will create barriers for acquisition (e.g., accreditation status will be required for US buyers) and burdens on the DAO (e.g., filing quarterly reports with the SEC). If BANK were deemed a security it would essentially destroy the token in its infancy.
Why does it matter that we have a strong argument against being deemed a security? Because regulations are driven by politicians, and politicians are motivated by power. DAOs generally, and Bankless in particular, are disrupting existing power structures. Therefore, we need our battle armor.