Sure, but there's a fact of the matter: It's not that we don't value the experiences or well-being of dead ancestors; it's that we hold that they do not have any experiences or well-being — or, at least, none that we can affect with the consequences of our actions. (For instance, Christians who believe in heaven consider their dead ancestors to be beyond suffering and mortal concerns; that's kind of the point of heaven.)
The "expanding circle" thesis notices the increasing concern in Western societies for the experiences had by, e.g., black people. The "narrowing circle" thesis notices the decreasing concern for experiences had by dead ancestors and gods.
The former is a difference of sentiment or values, whereas the latter is a difference of factual belief.
The former is a matter of "ought"; the latter of "is".
Slaveholders did not hold the propositional beliefs, "People's experiences are morally significant, but slaves do not have experiences." They did not value the experiences of all people. Their moral upbringing specifically instructed them to not value the experiences of slaves; or to regard the suffering of slaves as the appointed (and thus morally correct) lot in life of slaves; or to regard the experiences of slaves as less important than the continuity of the social order and economy which were supported by slavery.
Slaveholders did not hold the propositional beliefs, "People's experiences are morally significant, but slaves do not have experiences." They did not value the experiences of all people.
You know, I think you're wrong about that. They talked about how savages needed to be ruled by civilised man, and the like, rather than claiming that they were the same as us but who gives a damn?
When someone complains that utilitarianism1 leads to the dust speck paradox or the trolley-car problem, I tell them that's a feature, not a bug. I'm not ready to say that respecting the utility monster is also a feature of utilitarianism, but it is what most people everywhere have always done. A model that doesn't allow for utility monsters can't model human behavior, and certainly shouldn't provoke indignant responses from philosophers who keep right on respecting their own utility monsters.
The utility monster is a creature that is somehow more capable of experiencing pleasure (or positive utility) than all others combined. Most people consider sacrificing everyone else's small utilities for the benefits of this monster to be repugnant.
Let's suppose the utility monster is a utility monster because it has a more highly-developed brain capable of making finer discriminations, higher-level abstractions, and more associations than all the lesser minds around it. Does that make it less repugnant? (If so, I lose you here. I invite you to post a comment explaining why utility-monster-by-smartness is an exception.) Suppose we have one utility monster and one million others. Everything we do, we do for the one utility monster. Repugnant?
Multiply by nine billion. We now have nine billion utility monsters and 9x1015 others. Still repugnant?
Yet these same enlightened, democratic societies whose philosophers decry the utility monster give approximately zero weight to the well-being of non-humans. We might try not to drive a species extinct, but when contemplating a new hydroelectric dam, nobody adds up the disutility to all the squirrels in the valley to be flooded.
If you believe the utility monster is a problem with utilitarianism, how do you take into account the well-being of squirrels? How about ants? Worms? Bacteria? You've gone to 1015 others just with ants.2 Maybe 1020 with nematodes.
"But humans are different!" our anti-utilitarian complains. "They're so much more intelligent and emotionally complex than nematodes that it would be repugnant to wipe out all humans to save any number of nematodes."
Well, that's what a real utility monster looks like.
The same people who believe this then turn around and say there's a problem with utilitarianism because (when unpacked into a plausible real-life example) it might kill all the nematodes to save one human. Given their beliefs, they should complain about the opposite "problem": For a sufficient number of nematodes, an instantiation of utilitarianism might say not to kill all the nematodes to save one human.
1. I use the term in a very general way, meaning any action selection system that uses a utility function—which in practice means any rational, deterministic action selection system in which action preferences are well-ordered.
2. This recent attempt to estimate the number of different living beings of different kinds gives some numbers. The web has many pages claiming there are 1015 ants, but I haven't found a citation of any original source.