To be honest, if banks were the custodian of my cryptocurrencies, I wouldn't mind because the chances of my crypto being lost is going to go down drastically and if it was in an unlikely event got lost, the banks will have sort of insurance that will be in place to take care of the losses.
nooo. maybez your chance to lost is down, but it never happen to the bank that take your coin, risk still risk, they have same amount in every member.
dangerous happen if people do money laundering, eliminate evidence of negative actions that have been carried out, and the other thing.