Deliberately though. When an animal (collection of interworking and specialized eukaryotic cells) eats, it is doing so based on very specific chemical and physical signals. It's not that viruses are worthy, it's that they are aimless and directionless in their "existence". A prokaryote moving towards chemical signals and changing gene expression to consume nutrients to further purposefully divide is not the same a virus that happens to have the right configuration of proteins and genetic information to attach randomly to whatever has the correct antigen to allow for assimilation and replication.