What will be some of the unseen downsides to cryptocurrency becoming mainstream/fully adopted.

We love to talk on here about how good the future will be once we achieve mass adoption/integration of cryptocurrencies into the world and the financial systems that we currently know, and whilst I think there are many great reasons for this to be true (self custody, lack of manipulation by central banks/governments etc) surely as we all know history can paint a different picture when viewed in hindsight. What are some of the more unexpected downsides to a potential move to crypto in times to come? Things that most people won’t necessarily have thought of? Who would or could potentially loose out to crypto and who would be most negatively affected?