I think it's not that hard to make a definition of life that includes everything most people consider alive and excludes everything else. You could just call life anything that stores instructions for making more copies of itself on nucleic acids. Maybe I'm being too glib, I dunno. But the better definitions of life don't really seem to be trying to determine whether edge cases should count as alive or not, which as you note is not really a pressing question.
It's more a matter of saying, "This thing we call life is interesting. What are the characteristics that make it so interesting?" and coming up with things like self-replication, homeostasis, metabolism, that stuff.
I agree that it isn't that hard. But your definition doesn't quite do it. As written, your definition includes things that have died and things that aren't yet alive.
Dead plants and animals still have usable DNA for a while after death. If the tissues are preserved, sometimes it's a long while. And mostly, we don't think of spores or viruses as living things, but they certainly have DNA.
I would supplement your definition by saying that we refer to an organism as alive when its pieces are functioning in a coherent and mutually-dependent way to keep the orga...
Recently, Hank Green posted a video discussing the definition of life. He offered two definitions; that life acts in a manner to achieve a goal, and that life continuously decreases internal entropy.
There are problems with these definitions. The first definition includes every machine that has a function. The second one includes, for example, a machine that constantly reshapes parts of its body into a paperclip.
Other definitions of life are equally confusing, doing things like excluding viruses because they use other cells to reproduce, despite meeting the intuitive meaning we have for life.
So, dissolve "life." Why do we care if something is alive? To decide if its life has value. Hank dances around the issue, showing that life has no inherent value by using mouthwash to kill billions of bacteria in his mouth. But, he doesn't take this to its conclusion. It doesn't matter if something is alive or not. We won't suddenly care about the well being of viruses if a new definition of life comes along tomorrow pronouncing viruses to be living. What we value is sentience.
Bugs are extremely low on the sentience scale, so we feel free to kill them. Animals that are higher on the scale, such as cats, have laws preventing any sort of mistreatment.
tl;dr: Life is an ambiguous term, use sentience to describe a being's value.