It's bothered me for a while now. I understand why a parasitoid would do this, as it only temporarily requires the host, and that not all parasites kill their hosts.
There seems to be no evolutionary advantage in killing a host, because the parasite relies on the host for resources. Yet some organisms, usually microscopic pathogens, seem to fatally damage the host with no immediate benefit to themselves. Why is this?
I know this is asking for a broad soft answer, but I don't want the question to get bogged down by a specific species, although bonus points for using examples.