Actually considering ethics in science isn't what I'd call a waste of time. If we'd done that more in the past, we might not have walked into some of the shit we have to worry about today.
And as for the start of life argument, I don't see what conception has to do with death. I presume you're talking about the issue of determining if someone is really "dead" who is in a vegetative state and how that's the same as being a non-thinking bunch of cells.
It's actually not really all that difficult to separate the cases. We are all a "Ship of Theseus". A human isn't a single three dimensional object or set of objects, defined by immutable characteristics, a human is a process. We have a beginning, middle, and end. In that process we look different and are probably composed of significantly different matter, but we are still a "human" if we proceed from beginning to end as a human. When that process terminates beyond our the ability to restart it, then that human is dead.
As a human if you're irreversibly brain dead at any point after the development of an actual brain, you're not going to turn back the process. Not only that, but your brain needs to continue to operate for your fully-differentiated body to survive. You cannot go back to being able to live without the organs you have developed.
An embryo may not yet have a brain, or differentiated organs yet, but unlike a brain-dead individual, it can continue the process or living normally, if allowed to continue to develop. The fact that an embryonic form of a human needs to depend on the internal environment of a mother at that point is no more unusual or special than the fact that we need to live in an oxygen-rich atmosphere that protects us from radiation and other hazards of deep space. We are just in a form that requires that sort of environment to live in until we can transition out of it.
We remain an individual human process proceeding normally though our "execution". Humans may look like the inputs and the outputs, but what we really are is the running instance of a program that manipulates our environment. Although that may have connotations of a "soul", the idea is nothing more than what we see running on our computers every day in another form and while it does not disallow this from being a "soul", it doesn't require that religious element to be involved for it to be real.
So, very simply if the process can no longer be maintained in a running state, then that person is well and truly dead. If that process proceeds down even what appears to be abnormal lines, but it is able to continue, they are "alive", albeit outside optimal parameters. No matter the stage of development, or the result, I'd argue you should consider such a process to be a living human and ethically treat them as a human.
It is important to state that "ethically treating someone as human" doesn't preclude ending that life in extreme cases, or making alterations, but it does require us to at least make that decision about a person as if they are a person, and not as an un-person or as a "thing". That is the key point. You can use or dispose of a "thing" almost at will. There is a higher standard for disposing of or making use of a "person". Historically, most cultures have tended to want to make this distinction, and for understandable reasons.
The concept of starting "life" at conception is simply the logical place that an individual human process begins. A human sperm or an egg will not become an individual human. Nor will the dead matter that used to be a human nor will that matter which is the castoff of the process of human life. When it ceases to continue to contribute to the process, it is no longer "human". Cut your arm off, that arm isn't a human because it can't maintain human life on its own apart from the rest of its body. An embryo, though many, many times smaller than an arm or even a fingernail, is fully capable of maintaining the normal processes of life as a human in that state.
In the context of this situation, life beginning at conception simply means we need to treat genetic modification with the same ethical care we would for any other human. You can still suggest that the ethical considerations would allow the procedure, but you should start with the consideration of the subject embryo/cells as a human, and not as a thing.