There are many ways to assign value and measure worth. If the measure of worth is speed, then a cheetah or a gazelle has more value than a human or a chicken. If the measure of worth is suitability to agriculture, then most of us would say that cattle and chickens are more valuable than grizzly bears and mountain lions. If worth is measured by size, then giraffes and whales should score high on that scale of value. If you value money, then your bank balance (or lack thereof) is the measure of your worth. Value exists mainly in the eye of the beholder. Animal rights theorists often claim that all sentient animals deserve the same rights. In animal rights theory it is sentient life that is valued. As a measure of worth, sentience is as subjective as any other measure.
All living beings -- not just the sentient ones -- attempt in various ways, from very basic to very sophisticated, to defend themselves from attack and injury. All living creatures ordinarily attempt to survive and reproduce, so all living beings can be said in some manner to value their own lives. Animal rights theory grants equal rights to all sentient creatures -- a chicken and a human, for example -- yet totally disregards the oak tree that has a lifespan* longer than the chicken and the human combined. Moreover, it disregards the fact that plants often have quite highly developed self-defence mechanisms. Why should the value of life be measured by sentience? Why does being able to feel pain make a chicken more worthy of having rights than an oak tree? It seems like a rather odd way to dole out equal rights.
For last night's supper I ate the roasted breast of a chicken with some steamed vegetables on the side. Total monetary value of the meal was about $2.50. That includes the cost of the vegetables. The chicken I ate could just as easily have died in a hawk’s talons or a fox’s teeth as at a slaughterhouse. I do not doubt that a chicken in its own way values its life, but I will never be convinced that sentience confers on it the right not to be eaten. Animals that given the chance will eat humans pay no heed to the fact that humans are sentient. Sentience may enhance an animal's ability to evade predation, but it does not give the animal the right to immunity from predation. There is no such right. Not for humans, not for any animal. Not even for lowly non-sentient vegetables.
People like Mr. Francione can freely choose to be vegans if they wish. But Mr. Francione has not yet managed to abolish animal agriculture, though that is his stated mission. So those of us who choose to eat meat can continue to do so. It is always nice to have the freedom to choose the food you eat at your own table. Some of us value that freedom, too.
* The oldest oak in Britain is an English Oak (Quercus robur). It is estimated to be over 1,400 years old.