Variables that need to be established (Or, at the very least, should probably be agreed upon for reasonable discussion to occur):
Capabilities of GM - I think we can agree that the really interesting GM is the radical kind: Disease screening and elimination, physical attributes, lifespan extension, etc. Screening for genetic disorders is already doable; it's easy to imagine the ability to fix those disorders. We've similarly identified genes that are related to height (although height is one of those attributes that is tied to multiple genes, so precise modification of height would be tricky), eye and hair color, predisposition to obesity, alcoholism, so on and so forth(1). Lifespan extension is a subject
I've discussed before. It's a tricky one because many of its foundations are inherently tied to cancer, but I think it's fair to say that by the time effective GM comes around we'll have ideas on how to extend our lives - if not indefinitely, at least by a significant amount.
Availability of GM - Most of the contention seems to derive from this. It's fair to assume that GM will initially be extremely expensive and inaccessible, just as pretty much every new technology is. That said, it's also completely reasonable to assume that availability will increase exponentially with time, in the same way that availability of automobiles, computers, and more recently
genome sequencing did. Barring an intentional attempt to limit access - which I find somewhat unlikely - it seems likely that GM would become highly accessible very quickly(2).
When does GM happen - Will we be able to perform GM only before birth or at any time afterwards? In terms of the radical GM being discussed it seems reasonable to me that the most effective way to accomplish this would be
very early - as in, as soon after conception as possible. In this situation you'd only have to modify a small number of cells that would then divide and differentiate into the eventual person. This is how contemporary GM works. Attempting radical GM on a person would almost certainly be significantly more difficult - not only are you working with an
obscenely large number of cells, there'd also be other issues: What would the effect of making radical changes in mature cells be? Would it be possible to modify
only human cells without affecting the bacteria that make up the human microbiome(3)? Related; how would the normal human microbiome react to such modifications to their host? Although these issues are by no means insurmountable, I suspect that (at least initially) widely-available GM would avoid them by being pre-birth only.
Does the advent of GM also imply significant advancement in other fields? - This one's actually very important. Many of the arguments against GM seem, for some reason, to assume that other fields remain either locked in their current state or, at most, are progressing very slowly. For example, the overpopulation argument assumes that we are unable to leave Earth and therefore are limited by its resources. The related "how will we feed everyone" argument assumes an inability to solve the problem of food production/distribution - which, given the fact that GM is the ability to
modify life, seems a little far-fetched. This variable is tricky because it tempts a
deus ex machina "oh, but we'll have found a solution for that!" response to anything and everything. While locking all other fields into their current state is an efficient solution because it gives everyone common ground, it simply doesn't seem like a realistic prediction of the context that GM will exist in.
Bored of typing now. Will address actual arguments and their merits at some other point. Probably.
(1) At this point I'm obligated to mention the nature/nurture issue.
Few attributes are 100% determined by genetics. Upbringing and lifestyle can make a "genetically shy" person outgoing, a "genetically athletic" person obese, etc. Genetics should
not be considered the end-all of defining a person, a point which needs to be considered heavily when you consider many of the ethical issues with GM.
(2) Although probably not available to 100% of people (barring radical societal changes), which is where you could potentially get a 'classist' argument.
(3) The human body actually contains
more bacterial cells than human cells. Although our ability to target certain cells for treatment is improving quite a bit, I suspect that this point alone would be a serious obstacle.
