You can understand why the Church of England and the Catholic Church in England are in a tiz about it.
Children are born from a union of a woman and a man, bound together in holy matrimony. Sex is a necessary evil to make babies that can only take place after a church has sanctified a relationship in the eyes of God. Just as same-sex relationships are abominations in traditional/literal readings of the Bible, and sex outside of marriage is also something Very Bad Indeed. Stands to reason that babies made from three parents, of being born not of one woman but two, falls foul of the holy screed.
And yet what's interesting are the grounds the CofE and CCE are choosing to oppose the draft legislation due before Parliament tomorrow. The BBC quotes Rev Brendan McCarthy, the CofE's adviser on medical ethics saying ,"We need to be absolutely clear that the techniques that will be used will be safe, and we need to be absolutely sure that they will work." Then comes a line about having the necessary ethical debates. In what looks like a bit of coordinated messaging, Bishop John Sherrington of the Catholic Church is quoted as saying "No other country has allowed this procedure and the international scientific community is not convinced that the procedure is safe and effective ... There are also serious ethical objections to this procedure, which involves the destruction of human embryos as part of the process."
This is very smart positioning by both churches on this debate. By leading with the scientific uncertainties around the process they make the inevitable theological follow up a bit more palatable. True enough, there are unknowns associated with the procedure - even though the genetic contribution from the "third parent" is a minuscule 0.2% of the resulting embryo's genetic make up. That said on the balance of that figure and a review of evidence so far, the balances of probability of abnormalities resulting from this procedure have to be vanishingly small.
What the churches have done is to seize upon the presence of a third genetic donor and - misleadingly position them as if they're an equal party to the process when they're not. They're relying on the wider public, including MPs due to debate the bill, who are interested/exercised by the ethical questions around fertility and genetic medicine to not be as equally well-informed by the actual science underpinning it. In other words they're spinning a story, quite adroitly, that appears to take up the science but uses that as a draw bridge for the theology to march across. That's fine, the churches are part of public life and should freely voice their opinions on public issues. It's just a shame they feel the need to bear false witness to do so.