Abstract How can documentary heritage institutions protect the rights of publishers and creators while archiving their digital works for future generations? Is such an intervention of collecting, archiving and making available digital work justifiable and, if so, why? A legal deposit system is implemented in most national libraries to balance protecting rights holders and guaranteeing public interest. However, the expansion of collection coverage such as e-books and social media content has resulted in legal and ethical conflicts. Legal and economic approaches can convert legal conflicts into analysable trade-off phenomena. Therefore, we explore whether and to what extent economic reasoning applies to the legislative process. This is primarily for electronic legal deposit systems, specifically focusing on copyright and privacy issues. For copyright, legal deposits serve a public domain function and a correction function for market failures. Preserving the function of legal deposits can mitigate legal and ethical risks over time. However, such risks remain, as long as privacy is subjective and contextual. Even if documentary heritage institutions are granted legislative authority to collect digital work mandatorily, they must pursue other methods to minimise such risks. This suggests that collection coverage diversifies between countries and regions.