it's irrational for someone to buy 1 SBD for more than US$1; and the ecosystem was designed assuming people would act rationally, so all of the safeguards were built assuming the SBD might need to be pushed up.

That's true but sadly for us markets are not rational and the safe heaven function for an SBD is therefor not working at the moment.

And printing more SBD's is not that easy when the STEEM price goes down as well. (I get more and more liquid STEEM for my posts in the paypouts).

All those SBD's need to be backed in the end by STEEM.