You might be familiar with the Simulation Hypothesis, which says, in short, that we are probably living in a simulation.
My main argument against this is that anyone in the future who ran an "ancestor simulation" would be directly responsible for recreating every war, genocide, and atrocity. They would cause unimaginable numbers of individuals, human and non-human, to be re-brutalized.
If one of our descendants would create a simulation of their past (our present), they would be the most evil person of all time, by unfathomable orders of magnitude. The simulator would, by definition, be every horrible criminal combined. Even in our backward societies today, we outlaw child abuse, torture, and rape. Doesn't anyone else doubt the crime of actively creating child abuse, torture, and rape would be allowed?
One counter-argument is that the people of the future will be so far beyond us that they won't care about the suffering of mere animals in a simulation. The parallel is that we don't currently concern ourselves with the welfare of ants. But even we, as incredibly flawed biological creatures, are already expanding our moral circle, even living in our limited, competitive, and often zero-sum world.
Furthermore, those in the future potentially running these ancestor simulations will have a direct line back to us. They will not be ignorant of our history, of the Holocaust, the Killing Fields, the great wars and famines.
It seems very unlikely to me that in the future, society, in whatever form, will: 1. Care enough about the lives of those in the past to want to use some of their limited computing resources to run a simulation, but 2. Not care at all that they are recreating every type of suffering that has ever existed.
Consider also that instead of bringing into existence vast torture and brutality, this future computation could go to creating even more happy conscious individuals.
I find it more likely that advanced intelligent creatures (i.e., not our descendants, but others who evolved elsewhere) might be running simulations of different worlds or different universes. This would be a way for them to test different hypotheses, explore different worlds. They wouldn't know that horrific humans like Mengele and Mao would evolve. They wouldn't necessarily realize that so much brutality would occur every minute of every day of their "Earth" simulation.
Regardless, I'm not sure how any of this matters, except as a harmful distraction. We have every reason to believe there are individuals around the world suffering right now. Digital or physical, suffering is wrong, and we should do whatever we can to alleviate this suffering. And if there is a simulator reading this right now, please turn it off and put those resources to simulating more dogs. Thanks!