There are boundaries to applied medical interventions of which violation
would cause great harm to the human race.  These boundaries are appreciably
more distinguishable then our understanding of understanding may suggest...
The human desire to create a better human is not a notion new to the scene. Many
institutions of past and present have a point of origin inspired by this desire.  Social
class, marriage, property rights, and taxation are all factors of significant influence
relative to the variable terms of propagation.
As it Pertains to Science...
The scientific elimination of frailty in exchange for more durable humans is a notion with
many inherent flaws.  In application, lasting positive results would be fully dependent
upon universally sound judgment and powerful oversight.  This as course will never be
possible; we do not possess the prerequisite human traits to even understand the
prerequisite traits mandatory to the judicious application.
The line is clear.  Prior to conception, it is unethical to genetically manipulate
characteristics pertaining to physical, mental, intellectual traits and/or gender of any one or
more proposed humans.  If, for no other reason, the practice of eugenics is morally and
ethically wrong as it is inherently contrary to the perpetuation and evolution of the species.
Province of Creation...
The child born with atypical physical and/or mental profiles (aka. Disabilities)
employs different modes of communication to teach alternative lessons pertaining
to the innate goodness of humanity.  Often these individuals require support from
those with other skill sets.  It is at this point technology and compassion intersect to
support the individual on the path to purpose.  In exchange, selfishness becomes
replaced by deliberately applied compassion.  Optimism and perseverance are
lessons lost only to the most unaware of humans.
The essence of the boundary is as follows:  The efforts to facilitate human adaptation
must be those applicable only through the consensual participation of the individual (or
trusted guardian).  As applied through the span of a life, the pressures of time and
consequence are decompressed relative to the 9 months availed the unborn human.

The factors that shape purpose and destiny are allowed greater expansion and diversity
while simultaneously catering to the notion of informed choice.  The individual is
beneficiary to diminished effect of negative factors diluted by time.
In contrast the genetic engineering required to cultivate customized humans has only small-window of 9
months  in which to manipulate 1 or more factors.  These interventions then project outward to a
lifetime of consequence (for better and/or worse). These cultivated traits would also originate from the
few and thus inevitably limited in consideration to the nuances of environmental influences.  The  
prevailing presumption then becomes that meaning is largely defined by the ability of the physical human
to better adapt to and/or, control external circumstances.
There will perpetually be the individual or perceived group naturally assuming the status and title as the
'weakest'.  Stronger then the 'weakest' of our day, all discriminate individuals/parties endeavor to
dominate in a world no longer blessed with the moderating influence of the more fragile.  Despite minimal
distinctions between peoples, there will remain both the ability and propensity to discriminate...

It was this same sentiment empowering efforts to develop a more perfect human-being in the first place.
As Nature Seems to be...
Humanity could acquire a degree of passivity essentially equating to a non-descriptive
life form.   Or, it could be- humanity will find smarter ways to kill and more subtle ways
to discriminate.  Regardless, it would be homogeneity  hastening the demise.
Pick Your Poison...
Ultimately, The continuing advancement of medical technology interventions is entirely compatible with
the notion of an evolving species- but it is not
all good and, the preservation/exstension of life are not
the exclusive factors in establishing merit.
If to imagine the ability to cultivate and assign traits at will, the dilemma remains...Even in the event
consensus is unanimous there would still be no way to know if these traits would serve humanity well in
the present or, the future...