I don't see where any of that has anything to do with the human body being unique or special. Now the notion that many regions of earth have not advanced beyond the 20th century does have some weight though I wonder what they're doing to delay advancement considering how many ships humans have and the size of them as well as the space colonies. If our planet is that lacking in development it seems we need to invest back at home more.
As for people being unable to afford the genetic augmentations. I don't agree with the mentality that just because some people can't afford something others shouldn't be able to make use of it. Should we all be restricted to four cylinder cars because some can't afford a nice heavy duty and they're better for the environment? I much prefer the free market approach and would like to see those that own large vehicles taxed on them for dumping more pollutants into the air. The same could be said for genetic engineering in ME spell special licenses to allow for certain levels of augmentation the extra money could then be used to bring more people up to speed.
The long term concerns I do agree are a valid concern. That is if the change can't be reversed.
Of course cybernetics have even less of these concerns. After all the benefits flat out can't be passed onto the children of the parent. As we're dealing with a setting with cloned organ systems a person could even be restored to normal with some surgery. It'd probably be very expensive but doable.
Your fear of genetic engineering reminds me of when people set back medical science as studying corpses was taboo or illegal and people were uncomfortable with the idea of a heart transplant. Well and in more recent times the resistance to stem cell research.
Oh yeah like legislation ever worked. US continues to drive around with huge engines eating buckets of fuel and still not signed any of the environmental regulation like the Kyoto ones. Same goes for China, dumping millions of tons of CO2 and other **** into the air because they use huge quantities of coal. Or the various legislation about tax that rich people can easily evade because they have enough money to hide it somewhere. Or how about corporations that use much cheaper labour in countries where the legislation about worker rights or environment is simply not there. Yeah the so called "free market" and corporations which are basically rich enough to fund entire countries are certainly not doing anything illegal or morally questionable. As if the so called "free market" has done any favours to the people in the countries which are exploited by the richer and more powerful ones. Or have you forgot how when the banks, investment firms and the like were crashing and burning the people whose fault it was are not that affected by it. Here in UK while the bank that has nearly gone bankrupt was being bailed out by the government with the taxpayer money the people in charge of the bank who ran it into the ground were still getting their million pound bonuses. And that is still happening.
So no, we cant rely on corporations or "free market" to steer us the right way or do anything as important as human genome modification. The whole world is still in economic trouble because the US style economy that was so popular only works up to the point which had been passed a long time ago. US style economy only works where there is enough people and markets to be exploited by it, otherwise it crashes like we have seen multiple times already in the past century. So giving them control over something like human genetic modification with the barest of boundaries would end up in eventual enslavement of everyone that was not rich enough to buy those mods.
As for cybernetics, I am all for medical applications but cutting off your own bits and pieces to replace them with artificial ones? That is wrong. Imagine if 30 years from now your daughter decided that she didnt like her own legs, so she wanted to go down to the clinic, cut them off and get them replaced with artificial ones that would make her faster and be nearly unbreakable. Would you think its a good idea then?
Or how about a sitation where a criminal has gone and replaced his arms and torso with high performance models, so now he is quite bulletproof, can rip a natural arm off easily and so goes on a crime spree until they manage to stop them. How many people would be killed and maimed in the process.
Look at the whole gun control issue, US has nearly as many guns as people in the country in private hands. Does that make anyone less likely to get shot? Look up murder rates by gun in US and UK, and UK has many more times the population density.