Well of course. Everything's based on how you define things. If I say that you look terrible in black, whether or not you will agree with me depends how you define "terrible" and "black". If I remark that the sky is blue, you will agree or disagree depending on your definitions of "sky" and "blue". That's hardly a point worth making.
Some words we assume to have the same meaning, such as sky, blue, black, ect. Other words though we do not, such as person, male/female even death. Every debate of Plato's which I have ever read had a great portion of it depending upon definition.
See, if I think pain is X, and you think pain is Y, and you say Y, but I am thinking X, then we can have a major conflict. So would say that it is a point worth making.
In any case, my argument was that embryos are not subjected to any more pain, if any, when used in stem cell research than they would be if simply discarded. So whether or to what degree they are in fact capable of experiencing pain is not important.
Look at your initial example. You were saying that experimenting on embryos because they are going to die anyway is the same as experimenting on Jews because you're going to kill them anyway. My primary response was that the distinction between your example and the problem at hand is that the difference between the degree of pain, if any, that an embryo will experience when being experimented on, and that which it will experience when only discarded, is negligible.
Experimenting painfully on adult humans, and then gassing them, is clearly worse than just gassing them. In the former case you are inflicting more pain and suffering. That is why it is an unpleasant thing to do. It has nothing to do with some vague notion of human rights.
I am not trying to put words in your mouth, but would you say it is worse to experiment on a human if they were thus killed in a different way. Here is a example to better explain.
Person A will be killed by a gruesome method which is 'worth' 1000 'units of pain'.
Person B will be experimented upon by a somewhat gruesome method, 'worth' 700 'units of pain', but will then be killed by a much easier method (let us just state that this is a byproduct on the research) 'worth' 150 'units of pain'.
Also, what happens if others' pains are considered. Experiment on person A and cause 10000 units of pain, but use the results to remove 10 units of pain from 10000 people?
But that is a matter of rights and not pain per se.
Do you believe that a human baby has a right not to be tortured, but an adult chimpanzee does not? (Let's suppose for the purpose of argument that the baby and the chimpanzee have a roughly equal capacity to experience pain.) If so, why?
I'm not following here.
But the only explanation I can offer is that someone may think that the human species is 'less than' other species. I don't think that, so I can't explain why.