Let me start off by saying I am not religious, but I do think there is a point at which "playing God" (a term I feel awful using) can go too far. There are so many amazing things we can do with this discovery, we could create viruses that target only cancer cells, regeneration for burn victims or amputees, auto-immune diseases can be stopped in their tracks with cells resistant to the immune systems attacks. But there is most certainly a trade off. I fervently hope that every government -does not allow- the military to have any acess to this research beyond its healing capabilities. A bio-weapon constructed with this technology would have massive repercussions. I fear the possibilities that this research has in the wrong hands more than I fear the power that many countries have this very moment to send the world into a nuclear apocalypse.
I also hope that they research the shit out of this, and do not use it for medical purposes until we know -exactly- what we're dealing with. In my previous example of the benefit it could have fighting off a auto-immune disease such as MS, there is also the danger of creating a new cancer cell. Resistance to the body's immune attacks beyond what is currently available to a cancer cell is quite dangerous.
Although, if the scientists can construct synthetic DNA similarly to a programming code, with a possible "back door" it would be pretty cool. For example if they designed the cell to stop respiration and die off when introduced with a very specific chemical compound, one that is easy to make, but that would never normally be found in the human body. Perhaps a synthetic hormone our endocrine system cannot synthesize. Once again however, this leaves opportunities for misuse. If someone wished to harm another person, and they knew that their target had synthetic cells in their body, they could potentially use this back door and inject them with the chemical against their will.
Besides the obvious physiological dangers, one has to consider the effect it would have on our culture and society. If cells can be designed to be impervious to aging, and humans really do gain the ability to live if not forever, significantly longer than currently possible, one has to consider what effect this will have on the human race as a whole. Longevity comes with longer memories, and longer memories means longer held grudges. Any current animosity between nations could extend way farther into the future than it might otherwise, and long held tension is never a good thing. Besides that, if people live considerably longer, it also means that people will begin maturing slower, and having children later in life due to the fact that their biological clock just got rewound centuries.
If we have a society where there are less children and longer lived people we may observe a drop in crime, and it is possible people will be much more peaceful due to the wisdom that age often grants. However we will stagnate. In order to maintain a sustainable population we will most definitely have to have less children, and with slower or non-existent new generations we will "evolve" less as a society than ever before. In the past century we have experienced a huge gain in technology, life expectancies and have progressed significantly as a society. 100 years ago women were essentially servants (early 20th century America). Now they have more equality than ever experienced in the history of humankind, although it is not nearly perfect. Yet, 2000 years ago the role of men and women was practically unchanged with roles 200 years ago. How will our culture grow and progress if we do not have the new blood to take over when we are through? If we all live forever, I believe that we can expect to see a gradual shift into a society without difference. Gender, race, and social status will mean nothing. This has the good effects of bringing equality and quite possibly peace to the world, but one has to consider: Who are we without our differences? Would you enjoy an MMO where every class was the exact same? Where all the stats gave you the same bonus? I would not. I would -hate- to see the world become a bland, uni-culture.
I apologize for... Rambling... >_>