You can argue that we started "altering" evolution a long time ago when we created medicine to keep the sick alive. I think that technology and bio-engineering have, in a sense, become the new human evolution; we don't really rely on natural selection anymore.
That being said, I'm pretty open to genetic engineering. I wouldn't try to create a superhero, but I'm all for increasing disease resistance and intelligence. We finally have the technology to build humans with super strength and speed, but we don't have any need for those traits anymore
because of our increased technology. What a paradox!
I recently went to a talk with Ray Kurzweil, a big supporter of this idea of transhumanism. He demonstrated some really mindblowing stuff, but one that stood out was an artificial red blood cell. It's a tiny device that performs the same function as our natural red blood cells, BUT it's about 1,000x more efficient. So, you get injected with a few thousand of these things and you can now hold your breath for an hour. Asthma and other respiratory deficiencies will be eliminated. He made it sound like we'll have all this stuff to look forward to in the future, but then revealed that this is in animal testing as we speak- it will be used in humans before next year. Ray's endgame? To live forever.
I personally don't want to defeat death and live forever, but I wouldn't mind a few enhancements
I'm in favor of general modifications (disease resistance, super efficient respiration) for unborn children, but I think it should be their own choice later in life to be outfitted with gills, laser vision, or immortality.