So, dissolve "life." Why do we care if something is alive? To decide if its life has value.
I don't think that's the only reason we care. There's a lot of mostly-true generalizations that we can make about living things -- they require energy to keep living, they have some means of internal self-repair, etc. If I ask whether a vaccine has live or dead bacteria, it isn't because I value the live bacteria more, it's because it lets me assess risks more accurately.
People routinely value non-living things over living things. For instance, many people wear fur. (Or for that matter, cotton.)
What we value is sentience.
This isn't really true either. We have lots of different values. For instance, many people are willing to kill mice to feed their pet snakes. I don't think they'd be dissuaded if it turns out that mice are "more sentient" than snakes by some metric -- they like their [distinctive] pet more than they like the mice, which from their point of view are[interchangeable and replaceable.
We also value rarity -- consider a rare lizard versus a common bird-of-prey.
And we value several kinds of instrumental utility -- foxes might be smarter than chickens, but just ask a farmer which they value more.
tl;dr: Neither life or sentience are strongly correlated with how much most people value something.
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.