I think for me it's more a combination of a touch of the first of those (low personal estimated credibility for transhumanism -> lower estimated credibility of those who take it seriously), and that I tend to distrust large grand plans or narritives in general in favor of more narrowly focused objectives. Big grand plans have a way of obscuring details and sending people off track and into tangents via ideology.
It makes a lot of sense for the Google people to be transhumanist, with Sergey Brin and Larry Page working with the Singularity University, but still I was surprised to hear this on the new Colbert Report (of the 23rd of April):
He seemed quite serious, too.
I guess a lot of people would take transhumanism more seriously if they heard the top people at Google are in. To me, I actually find it makes Google seem more trustworthy. In-group psychology is weird.
Here's another good interview with Eric Schmidt. No explicit transhumanism, but some fairly intense plans entirely compatible with it.
(edited: corrected title)