They aren't useless. They're worth a lot of money to the right person. This meme has repeated endlessly on reddit, all while there was an underground trade going on in verified, aged accounts with karma.
Right now on Kbin it may look like it's not important, but if Kbin grows and grows it's going to become a target for spammers, scammers, etc, and it's going to have to start to look for solutions on how to identify and restrict accounts. one of the simplest, and most obvious ways is the karma/rep system.
New account? Account with negative karma? May find it's rate restricted and posts are autohidden. Purchase an aged account with rep and you can at least spam for a bit until caught, then pay $5 for another account.
Thanks Ernest. I definitely think if we've blocked a user in a magazine the microblog shouldn't be picking up stuff from them, and we need to be able to turn on automatic hashtag pickup or not.