When you mention "serious abuse" do you mean the amount of STEEM power they control on the aggregate, or the aesthetics they create? I have never seen stats on how many of the free 15SP accounts there are, or how much they are actually downvoting and what the the financial impact of that is. Anecdotally it doesn't seem like a serious problem to me in terms of real damage, and it's more of a question of aesthetics. I could be wrong. Either way I don't think anyone really wants free accounts doing nasty shit on the blockchain, so I agree that it should be mitigated.