Lets look at a recent incident in the news. You have probably heard that a Chinese scientist did gene editing on human beings. This action brought great criticism from the scientific community. The man involved will probably lose his profession permanently, and it is possible that he could go to jail in China.
Now ... as part of the experiment he created 30 human embryos. Fertilized embryos, new living people, if you will. He analyzed them, chose 2 healthy embryos, and discarded the rest. What does that mean. It means that 28 embryos were killed. Two were implanted into human mothers. Why would he do this? Because he needed to check the results of his gene editing experiment, and he wanted to implant healthy embryos that will produce healthy children.
You can see that the ethical implications are quite big. Should a human embryo be treated the same as a frog embryo? Can human embryos simply be discarded? I am not sure about the ago of these embryos .. i am guessing they were a few days, or maybe a couple of weeks. They had multiple cells, but probably no development of organs or brains.
This was done. It is a fait accompli. And perhaps a small taste of what is coming in the 21st century, where our idea about the sanctity of life may be tossed out of the window entirely.
Finally, no-one knows yet if the children born in China from this experiment will be healthy, or not. It truly is an experiment, albeit an experiment on real human lives. Hence the great outcry about what was done.