I'm likely wrong as my only experience here is playing ksp, but I would think at no point in the ISS orbit would it be able to economically fire trash at an escape velocity, and I wonder if doing so would disrupt the ISS orbit. (depending on the weight of the trash)

That means it will stay around longer, thus will be a hazard longer. Allowing things to de-orbit and burn up on re-entry is a safety feature.