okay I haven't read all of this thread, so here is my pure two cents
YES. They is bad.
They may have evolved as parasites, but they didn't have to take a host. Having a host no way effected there live spans or reproductive capabilities, with is the evolutionary justification of parasites. They were doing fine before and without an array (honestly any) host fo years, so to decide okay, now we want host, and we're gonna take em; that warrants a time out.
It sucks that they are deprived so many things, but that's how they evolved, and it suited the passing of genes for sustainable live ; and that's the only requirement of evolution