The point was to make a clearly after-the-fact definition that works, but doesn't say anything interesting. There may not be any exocritters that use some other macromolecule for their genetic material. If not, it would be a non-issue, right?
If you try to make a definition that says something interesting, I think it's got to be a whole checklist of interesting characteristics of life in order to exclude things most people wouldn't consider alive. Then you get people looking at objects that exhibit some, but not all of the characteristics and wringing their hands over whether or not it's really alive, as if that's a thing. Which I still don't think it is. I think what we're looking at here is lingering vitalism.
Life is just matter with interesting characteristics. We can talk about why it's interesting, but we can't explain why it's totally different from all the other matter, because it isn't.
The point was to make a clearly after-the-fact definition that works, but doesn't say anything interesting. There may not be any exocritters that use some other macromolecule for their genetic material. If not, it would be a non-issue, right?
It would still be an issue if we started making synthetic life. A good definition ought to cause as little inconvenience as possible. I agree that life isn't fundamentally different from all other matter, but the reason we have the word at all is because it's handy to be able to encapsulate it as a reference class. ...
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.