For all the reasons that are no doubt discussed in biology classes around the world annually, viruses some life characteristics and not others. Putting them is a borderline category seems logical.
This is the first I have learned of prions; they don't even have genetic material, yet they "reproduce" more copies of themselves by causing other proteins to morph. Is that really reproduction? If I walk into a classroom and had a ray gun that would take other people and turn them into copies of me, am I reproducing myself? Not really. I am not creating new life, I am just changing existing life into a form that resembles me. I don't know that prions should be considered life-like at all.
Both these examples, though, generate great discussion regarding the nature of life...
I agree with Alison that viruses should be considered "borderline" living because they are acellular and do not carry out most of the characteristics of living things. The one thing that unites all living things is nucleic acid (which even the viruses and viroids contain), but prions don't even have that. They are ust abnormal forms of harmless proteins that are able to transform/ destroy other proteins and cause disease (like Mad Cow). I don't see how they could be considered living by any definition, otherwise proteins and other molecules should also be considered living things. It is interesting because the more we know, the more important it is to revise the definitions we've always held true, like what a "living" thing is. Along the same lines, I always enjoy discussing with my class not only what is living and non living, but when something stops being alive. With all the modern medical technology, you can really keep someone "alive" with their body hardly doing any work (and resuscitate too of course).
So, is it okay that scientists are split in considering viruses and prions living, is it that subjective, should we keep to the traditional definition of life (as being cellular, reproducing, transforming energy etc) or is it time for the definition be revised?