|I've been hanging out and engaging empathically with Transhumanists since before they tried calling themselves Extropians, so should forgive myself for sometimes feeling impatient with some who have come to H+ more recently.
For me, the Trans- part is from transitional (and not centrally connected to this forum), but it is the presumptions infesting the -human part that can trouble. Trying not to go too deeply into grey-armband points made in other posts, it is about attributing our high planetary impact to our collective action rather than any defining superior characteristic of the individual human animal, let alone triumphalist readings thereof.
Why I am not Agnostic is a work in progress which includes an aspiration to be "Humane but not Humanist" because, while I'm first to concede we have it very good and getting mostly better, Taleb's Black Swan (and particularly his turkey) show we are far far from confirmation of humanity's longer term significance. On the plus side of the ledger homo sapiens sapiens is close to the extreme generalist end of the specialist-generalist spectrum. While we are one biological species, we are rapidly fragmenting into no end of intellectual species, as we have since long before the metaphorical Babel. On the minus side, our individual needs are increasingly met by deeply layered systems of the collective with almost no concern as to how we might survive, let alone rebootstrap a viable social order from scratch. In summary, the jury of Big History is still out with respect to humanity and will be at least until immortals start finding unexpected ways to die.
Our continued naive infatuation with all that we think is human is also blindsiding us to a deeper reading of Kevin Kelly's 2010 provocation What Technology Wants which hints that our systems and technologies are more likely transhumanist than any update to the familiar human model. I'm in less of a panic than most singularitarians in that I'm neither persuaded by the efficacy of increased individual "intelligence" nor concerned that an individual Mule (to borrow from Asimov's Foundation) can change everything without collective support.
While Transhumanism is rightly a broad church, I am offended* that it is claimed to include David Pearce's nonsensical proposal for abolition of suffering. While I strongly encourage finding an exit strategy for factory farming and other abuses based on outdated prejudice that only human life is worthy, I'm equally concerned by Cartesian misconception that death is a kind of suffering (save for those "left behind" with unresolved dependencies). And I'm even more concerned about presumptions that our very short history of discourse, let alone Enlightenment, provides a moral perspective which should be universalised across every other product of billions of years of evolution on this planet alone. As a diver, I'm more aware than some that the marine food chain is almost entirely animal eating animals and that without viable oceanic ecosystems, life on land would be extremely precarious.
*Nobody, not even me, has any right to seek restitution for such offense.