> Are there any tenets of secular humanism that extropians or
> transhumanists outright reject?
I think that almost all traditional social belief systems
make a fundamental assumption that the human condition
is essentially stable on a human timescale. I think that
this assumption profoundly affects these "isms", and
usually has a greater effect on them than their explicitly
espoused beliefs.
I think transhumanism rejects this outright, and that
this rejection is the central transhumanist belief.