Imagine we are taking part in a panel of experts advising the government on the ethics of stem-cell research.
A succession of doctors explain the potential benefit in terms of lives saved and alleviation of suffering that cannot be achieved by any other means. An embryologist describes the blastula in detail, explaining how it is hollow ball of cells just a few days after conception. He tells how many of these are eventually discarded following fertility treatment and how millions of precious stem cells can be cultured from just one blastula.
Fertility experts describe how a very high percentage of fertilised eggs at this stage of development fail to implant are spontaneously aborted without the mother even being aware. It is also explained how one of the primary functions of contraceptive pills taken by millions of women is to prevent the implantation of a fertilised ovum. All are satisfied that there is nothing resembling a nervous system or consciousness at this stage.
All of these objective facts are presented along with mountains of laboratory results and images.
It looks like the advice will be unanimous when a theologian asks to be heard. He tells us that at the very instant of conception something called a human soul is implanted in the zygote by an almighty god. For this reason stem-cell research should not be permitted.
Reasonable requests for answers to questions about the nature of this thing called a soul are dismissed as a divine mystery. Objections regarding the soul/s of twins or chimera are similarly brushed aside with dogmatic statements about limbo and divine foreknowledge.
The theologian insists that his objective is the same as the rest of the panel - to maximise the well being of CONSCIOUS creatures, but he is unwilling to join the dots and explain how refusing a cure to tens of thousands of suffering humans will achieve this goal.
Why should the theologian's objections be given serious consideration in the panel's conclusions?
This is just one example of many we could use to illustrate point. We could discuss a prohibition of contraception that has resulted in incalculable suffering and poverty. It has saddled parents with huge families they can ill-afford and condemned women to decades of child-bearing.
We could discuss homosexuality and investigate whether religious objections amount to anything more objective than "god says..."
There is no absolute standard of perfect morality. We work out ethics from the bottom-up and nobody should demand respect for dogmatic assertions that are unsupported with objective evidence.