Most transhumanist ideas, would I think, leave humanity worse off. A few might lead to our extinction. Some, used ethically and intelligently and very carefully, might actually enhance life for us humans.
C. S. Lewis makes a strong argumetn against the ideas now called "transhuman" in his book, The Abolition of Man. Anyone concerned with these issues should read this philosophical treatise on the errors of the human idea of improving our world or ourselves.
Most of the problems that the transumanism movements hopes to solve have already been solved at lower cost through ancient arts such as qigong, yoga, and healthy eating. And cost is a critical issue, as the transhumanist movement tends to come up with very expensive solutions that are only for the elite, which creates ethical problems.
Nanotechnology is proving incredibly dangerous. Nanoparticls are creating cancers more horrid than even those that arise from PCBs and radiation.
We know far too little to be tinkering with the human genome. Let's study it for a few hundred years first. Tinkering with it now is like a caveman rewriting a computer program.
There is a law called The Law of Unintended Consequences: it's a warning about tinkering with any complex system, especially one we don't understand. And we are complex systems.
Isaac Asimov first proposed the Three Laws of Robotics to protect human beings. Then, in one of his later stories, he showed how this would not work. If we careate a sub-set of intelligent beings (human or robotic) that are a new species, they will inevitably out-compete us.
But it is far more likely we will not do as good a job as what nature has already created in the Paragon of Animals.
Let us learn to be healthy and wise. When every human being has a clean place to live, water, food, excellent education, freedom, and fundamental health care, then we can work on helping all of us step up together.