「なし崩し」を英語で言うと

遺伝子編集のトピックで見かけるのが'slippery slope towards the rise of designer babies'のようにslippery slopeという言葉。しかも、このような議論をslippery slope argumentというようです。

'Ban genetically modified embryos': Scientists call for global action, warning of 'slippery slope towards the rise of designer babies'
Scientists ask world leaders to prohibit the use of gene editing techniques
New report says it would allow parents to create 'designer babies'
The long-term effects of creating 'enhanced' people are not yet known
Advocates argue gene editing would get rid of inherited diseases
By LISA RYAN FOR DAILYMAIL.COM
PUBLISHED: 17:49 GMT, 1 December 2015 | UPDATED: 00:27 GMT, 2 December 2015

A group of scientists are today urging world leaders to ban the use of gene editing technology, warning it is a slippery slope that could lead to a rise in ‘designer babies.’
The concept of genetically modified human beings many sound like the plot of a science fiction movie.
But, scientists at the Center for Genetics and Society said in a new report that techniques for editing genes may soon become commonplace.
They warn it could lead to parents paying to ‘enhance’ their children – using gene editing, to make their offspring smarter or more athletic as they please.
Allowing the use of these techniques is dangerous, the scientists said.

辞書的には物騒な訳語となっていますが、「なし崩し」といった語感があるのではと思います。

（ウィズダム）
a slippery slope
すべりやすい[｟比喩的に｠(破滅へと続く)危険な]坂道

BBSのサイトでわかりやすい説明がありました。自発的安楽死を認めると、本人の意思に反した反自発的安楽死も認める流れになるというような議論をslippery slopeというようです。

The slippery slope
The slippery slope argument views decisions not on their own, but as the potential beginning of a trend.
In general form, this argument says that if we allow something relatively harmless today, we may start a trend that results in something currently unthinkable becoming accepted.
The slippery slope argument is used in discussing euthanasia and similar topics. For example, people worry that if voluntary euthanasia were to be made legal, it would not be long before involuntary euthanasia would start to happen.

といってもロングマンやオックスフォードでは「破滅への道」と解した方がいい文例が載っています。

（ロングマン）
(be on) a/the slippery slope
British English informal
used to talk about a process or habit that is difficult to stop and which will develop into something extremely bad
(be on) a/the slippery slope to/towards
He is on the slippery slope to a life in crime.

（オックスフォード）
the/a slippery slope
a course of action that is difficult to stop once it has begun, and can lead to serious problems or disaster
She realized he was on the slippery slope towards a life of crime.

この議論の言い分もよくわかります。先ほどの病気を治すために遺伝子編集を利用することに反対する人は少ないでしょうが、以下にあるように遺伝子編集を使って、赤外線も見える人間を作ろうとすることは行き過ぎのように感じるからです。

This point is backed by scientists, led by the head of the biotechnology company Sangamo BioSciences, Edward Lanphier, in a paper in Nature recently. “Permitting even unambiguously therapeutic interventions could start us down a pathway towards non-therapeutic enhancement,” he said. In other words, removing genes for fatal inherited diseases from future generations will result in humanity sliding swiftly down a slippery slope to the creation of generations of “improved” or “enhanced” humans with bigger muscle masses or higher IQs. Some could even be created to see in infra-red or ultra-violet light, it is argued
Defenders of gene-editing say this connection is simply not supported by the evidence. “You have to ask when people use the slippery slope argument is just how slippery is the slope, and just how bad will be it be when you reach the bottom,” said bioethicist Sarah Chan, at Edinburgh University.
“It is not clear the slope outlined by those calling for a moratorium is really that slippery or that things would be that bad if and when we reached the bottom.”

こういうのは科学的に決まる議論ではないので、方向性を自分たちが決めていかないといけなんですよね。試験対策から離れて、簡単に答えの出ない問題を考えてみることも必要かもしれません。