He was speaking as scientists began the process of trying to grow organs inside pigs in an attempt to solve the worldwide shortage for transplants.
Researchers from the University of California injected human stem cells into pig embryos to produce human-pig embryos known as chimeras.
How is a chimera created?
The embryos are created in two stages.
1. DNA is removed from a pig embryo - using a technique called CRISPR gene editing - to allow it to grow a pancreas.
2. Then human stem cells are injected into the developing pig, which scientists hope will force the foetus to grow a human pancreas
The human-pig chimeric embryos will look like a normal pig's embryo, but one of their organs - the pancreas - will be made completely from human cells, the team says.
They will be allowed to develop in the pigs for 28 days before the pregnancies are terminated and the tissue removed for analysis.
Dr Trevor Stammers, Christian and Programme Director in Bioethics and Medical Law at St Marys University in London, told Premier's News Hour that there is a fine balance between advancing science and caring for animals.
He said: "If the mothers of these pigs are needing to be killed in order to do these experiments that's something we ought to contest."
The experiment comes with a number of ethical considerations.
Animal rights organisations oppose these kinds of experiments on the grounds of the suffering caused to the animals and the prospect of organ farms.
The National Institutes of Health, a US medical research agency, imposed a ban on funding experiments like this in 2015.
Dr Stammers went on to say that when it comes down to ethics, scientists promising results they do not yet know is unethical.
"Scientists particularly when they get paid huge amounts of money from commercial enterprises to carry out experiments will say all sorts of things about the end result that they're hoping for - but there may not be a scrap of evidence in the first instance."
But he added that the ethics is all about balance: "You've got to balance the dangers of this work against the possible benefits, and as far as I can see at the moment the benefits are marginal."
If successful, the chimeras could potentially be used to grow not just a pancreas but hearts, livers, kidneys, lungs and corneas.
Listen to Premier's Antony Bushfield speak to Dr Trevor Stammers here: