There is a great ted lecture on this subject. I thought he did a good job at addressing the concerns. At least to the point of defending that research should continue to at least allow future generations to decide if they think it is acceptable.
http://www.ted.com/talks/aubrey_de_grey_says_we_can_avoid_aging.html
You didn't talk about any self-fulfilling negative correlations. A volvo doesn't prevent accidents, just makes the accidents less deadly, so it may actually be the more reckless drivers that take them so they can continue to be reckless (this effect may be much smaller though) or parents that choose a safe car for their reckless teen. Another example is when seatbelts were introduced, the owners of cars with them became more reckless because they thought they were safer, and actually ended up in more accidents (though the death rate of drivers remained a... (read more)