We don't even understand half the things going on in the human body,
it is not yet time to start screwing with it.
Disagree. I wholeheartedly support people conducting whatever kind of self-experimentation they like. It will never be a 'good' time to start screwing with the human body, and today we're at a point where the tools to do so are becoming pretty common/cheap (Compared to say, 20-30 years ago).
The whole mistake here is trying to make it a political movement and draw 'support', whatever that means, from people who have no interest in what they are doing. Transhumanism is going to happen regardless of the presence or absence of a political movement. The only possible political goal that I can see a large majority of the transhumanist population agreeing on is some kind of extra legal protection of peoples rights to do whatever they want to their body.