and also, you want people to send you bonds before you send them bitcoins - so it isn't really important if you trust the system, but it is only important if people who send you the bonds do trust the system, right?
The fact that you have bonds already shows you trust Goat. The bonds are just GLBSE's paper keeping for your money that Goat has in his Pirate account. Goat already has your BTC.
Whatever happens on GLBSE can be verified by Nefario and you cannot actually screw one person without screwing the others (including the guys from a Russian mafia).
While (100% hypothetically!) after I sent him the bonds, how can I prove that he paid me for them after all?
It;s much harder then and even if I can prove it, there will be no Russian mafia going after him because I'm not one of them