Spiders are alive. But we show no remorse in killing one. Or any bug. Or would we kill it if it were "alive"?
Plants are alive. But we think nothing of it.
We think of "life" more in terms of human and animal life.
Instead of thinking in terms of life, maybe we should think in terms of "human perception of sentience" since that is what seems to dictate what life forms a human will indiscriminately kill off or think of as "life" and what they don't.
Even among other humans, a human in a vegatative state (aka Terry Shiavo, for example) who can make noises, follow the hands in front of the face, is not considered "alive" and thus is killed off (ie. "plug pulled") becuase doctors and courts did not deem her as "living" any longer. Sure she was kept alive via machine (aka "cyborg" in the literal sense) but she was not considered "alive" and thus wasn't given the right to "live". Others were in this situation.
It was because of intelligence level? or ability to care for oneself? There are those with mental retardation who also perform in the same way, yet are considered "alive".
I think "life" is only subject to human interpretation. And also depends on WHAT human in POWER is determining the right to life.
This is the scary part.
We have come a long way though. For example, years and years ago slaves were not considered "alive". They were just meat that performed tasks and if they misbehaved, it was OK to beat them or kill them, just much like squashing a spider. Even though they had feelings, bred, ate, reproduced, spoke. They were not considered "alive".
I hope you see what I'm getting at. In summary, "life" I think is largely open to human interpretation and even then it depends on the individual human and the power the individual has in society to determine what is and is not life in a manor that others will be forced to (or believe they must) follow.
Down to the molecular level, technically *everything* is "Alive". Even the computers.
I had a conversation about the personality of cars with a friend of mine recently. We agreed that COMPLEX MACHINES can take on a "life of their own" or a "personality". In the case of cars, they adapt to their environment and they each behave differently, depending on the care they get and the interaction with their driver. They, as complex machines, "learn" and the patterns of their lives become "known" and a part of them. A car will behave differently depending on the driver.
My friend drives his wife's car and she drives his now as hers is getting VERY old and he can best handle the problems it might have. Plus she needs a good car to take care of people with disabilities. So, they kinda switched drivers. She told me that the times she does drive her old car, it just doesn't seem the same anymore after her husband has been driving it. It "seems different". That's because, we think, the car got used to her husband as the driver, and adapted it's "personality" so it's different.
People don't think cars are "alive". Though some who care for and even take care of collector or classic cars (such as myself, as I care for a classic that I dearly love, and some folks in my car club as well, who have classics and/or much cared-for cars) some of us do feel our cars are "alive" - in the sense that we recognize the car's "personality" and we can tell what it's "Saying" to us via engine warning lights and even the very sound of the engine. We can communicate, and undersand our cars that well. Though most don't pay that much attention. Just get it, it runs, it stops running, if the mechanic can't fix it for the right price, junk it and get a new one. Those of us who truely love our cars, we work on it, try to find the problem, even if it takes months, we keep at it, keep trying. Our friend needs us. Only if the car is truely falling apart to the point it's unsafe or can not really be fixed at all, do we say goodbye.
Now do we feel that way about our toaster? Our washing machine? are these devices as complex as an automobile? Nope.
The more complex (complex being the key here) the machine, the more likely it can take on a life or personality (or both) of it's own. Sentience NOT REQUIRED!
I do not believe sentience is required for life. An amobea is alive, a cell is alive. Neither is sentient.