I am not a witness or a whale but just a Minnow
You raise a valid concern but the whole aspect of user registration seems to be manual at the back end which requires diligent monitoring and validation by admins. Honestly this is a great platform unlike other social tools that sell your data and try to sell you AD's from others .
STEEMIT brings in the actual engagement that needs to be from a social platform with "Proof-of-Brain" . I know some of us are used to a quick entrance but having a valid authentication process eliminates bots and users creating accounts for mining , scamming and spamming.