it's true you can't make a non-XRP payment to someone unless they have indicated someone they trust to hold the funds. Just like I can't wire transfer someone money without knowing what bank they trust to receive the funds.
Extending your point: this is an important feature, not a bug. Without this feature, anyone could be saddled with TF's worthless IOUs rather than say Bitstamp IOUs or IOUs "issued" by friends and relatives.