There exists a particular cluster in thingspace which we call "living things" and we have invented a magical quality called "life" to apply to members of this cluster.

Virii are peripheral members of the cluster, just like penguins are atypical birds, so there's confusion. There's also general confusion about which dimensions should be considered important, i.e. complexity, intelligence, etc.

Discussions of the meaning of life are confused for the same reason as discussions about the morality of coffee tables.