I’m going to pretend that this makes sense for a minute, and bears any resemblance to what you no doubt believe is a scientific claim.
While it is true that an embryo is a clump of cells – so are you. Just a bigger clump. Cells, of course, differ, as well. What we are talking about is a particular kind of cells – cells with a unique DNA sequence – a unique combination of genes from mother and father. These cells are NOT genetically identical to the mother’s cells. They are NOT genetically identical to the father’s cells. They are a separate combination entirely.
These cells are a combination of the genetic sequences of the father and mother – and are just as unique as either of them are. Unless they have an identical twin, they will be just as unique, genetically, as any of their siblings would be – from their parents, and from each other. After their birth, identical twins have slight differences due to environmental factors – and then, they begin to differ markedly by their differing experiences – and, obviously, genetic similarity is not the only marker of ontological status – but if you are attempting to make a scientific claim, this must be understood.
They are not the father’s cells. They are not the mother’s cells. They are a newly formed, developing body – a different body – a life, a human, and a person that is demonstrably separate, as well as distinct from, that of the mother or father. Whether at the zygote, morula, blastocyst, or embryo stage, this is a unique individual. Preimplantation genetic diagnosis, for example, presupposes that this is the case.
If this argument is taken to its logical conclusion – what you’re actually saying is that the technical differentiation between the DNA of disparate individuals that you, on the one hand, think is positive, and remarkable – is, on the other hand, irrelevant to the very field in which it operates – because it doesn’t fit your argument. How does that make sense? How, my friend, is that scientific? If this is just “a clump of cells” – what makes you any different? This isn’t an argument. This is a fallacious misdirection, and should be abandoned as a serious response.