One potential drawback of adult collectors investing heavily in Lego sets is the financial cost associated with collecting rare or retired sets. Some critics may argue that spending significant amounts of money on plastic toys is frivolous or wasteful, especially when considering other pressing financial priorities. Another criticism could be related to environmental concerns, as producing and shipping large quantities of plastic toys contributes to carbon emissions and waste generation. Additionally, there may be societal perceptions around adults engaging in activities traditionally seen as children's play, which could lead to judgment or stigma.