You might want to read the wiki page on Transhumanism as well, since it does list in detail the schools that argue against Transhumanism and the pros the transhumanists have published. Just to be clear, transhumanism is not just about creating a completely new species of humans (as people seem to misconceive because of the pig-woman art). There is no 'them' and 'us', that's exactly what transhumanist thought is trying to remove.
- Supports the abolition of worldwide suffering, and providing standard civil rights for all.
- Supports democracy and liberalism in a hybrid form.
- May be able to end human disease and/or involuntary death.
- Removing gender lines (gives people a choice).
- Ability to affect the technological singularity (superintelligence) for bettering mankind (rather than say going matrix on us).
- If true, then technology can be invented to cure the world of Environmental issues.
- Much of the philosophy is too hard to implement and has a 'sci-fi now' mentality.
- Goes too far into the technological side as to override nature with technology (may cause worse overpopulation and food shortage etc, problems it will then have to solve).
- Blurring the lines of human identity (this might be a pro for some, I do advocate blurring the sense of 'us' versus 'them', but I think it should be as a result of voluntary elevation of consciousness, not genetics).
- Altering the democratic outlook (by altering events at a gene level, this is semi-alarmist).
- Playing god (I have no objection to this, Christians and people who believe in god would almost have to).
- Segregating people via genes (I will say that transhumanism tries to change the species as a whole rather than to the privileged few, but until it can do it to everyone, it's true that people will be segregated, Gattaca style).
- Corporate interest, since it is hard to control technology that can make money and prevent it from becoming a money spinner instead of a tool made for the good of the world.
- Eugenics is a bad word at the moment, and it is true transhumanism uses words like 'limitations', 'improvements'. When such matters are rather subjective.
- Too technology driven, many people agree with the central tenants of secular solutions for world problems, but become alarmed at the intent to do everything by raising human consciousness mentally as well as physically (brain changing).
I do think overall, the ideas of transhumanism suggests the supporters have worked out 'we're all human' as opposed to 'there's them and there's us', but instead of focusing on the overall understanding of that point, they skipped straight into the sci-fi books and started trying to build a Utopia from their understanding of human problems. While the initial thought is sound (people are just people), what came after is not so sound (so we need to biologically change people so people are better people). It also suggests some involuntary change to meet certain 'standards' of consciousness, whereas I advocate voluntary cognitive improvement (I also advocate giving people the chance to learn).
This is a shame, because I think the central tenants of this movement were good, the abolition of suffering, the elevation of the human consciousness as a whole, standardizing human civil rights and equality, putting more resources into researching technologies that improve rather than diminish human condition on Earth (clean/green technology). It just seems like it couldn't stop steamrollering itself from a moderate beginning into a radical/extremist sect to compete with other ideas. We're not even all ready for the idea that we're all just people, let alone the idea that all people must change to change the world, and even further, that someone needs to do the changing in a proactive manner.