Our natural body is gorgeous, a wonder of nature, but it's not perfect. Evolution tried to improve us, making every generation better than the previous one. But sometimes, during the evolution of a certain species, some mistakes appear (either because of a function that is no longer needed and individuals get evolutionary vestiges or because of the implementation of a new function that is not fully developed yet resulting in old stuff messing with "prototypes"(like the number and size of teeth that remained the same in spite of the maxillary that started to shrink over time leaving more space for the brain to develop) ).
Also, the mechanization of our body may offer us more abilities like seeing the ultraviolet spectrum, making us physically stronger etc..
Last but not least, it could also increase our lifespan. Just think about it!!!
Evolution may not be perfect, but it is progressive, as technology is also progressive. The argument is that technology will perfect our flawed human bodies, and yet, technology is not perfect either. It is also flawed. There will still be inconveniences from technology, such as battery life and replacement, among other things.
By believing that human bodies are flawed must be perfected, has shown to cause psychological disorders, such as eating disorders, body image disorders, and etc. In the case of plasic surgery, there are many people who undergo surgery, some surgeries even damages sensitive nerve tissues and cause permanient numbness, in order to achieve perfection. Some are even addicted to plastic surgery, they want to that look that they envision, regardless of risk.
If these same perfectionistic ideals were applied to mechanical biological hybids in order to perfect the human body, when is the cut off point for someone who has reached perfection? What if they have so many surgeries to mechanize themselves, that there's very little to no human left? Would they still be considered human and have human rights? Would they still be conscious?
Although, I absolutely love the idea of mechanized biological hybrids, and I hope that technology continues to advance to improve human lives, I don't believe they should be used in the ideals of perfection.