This is a good point. Ettinger and a few other cryonicists I've talked to are against uploading. My non-serious estimate is that this is perhaps half of cryonicists (who take a side), I'd guess more than half of CI and less than half of Alcor. On the other hand, many others like Mike Darwin seem to be more agnostic on the topic than anti-uploading or the reverse.

It's worth considering that keeping (significant numbers of) the original atoms is not necessarily impossible with fixation techniques, assuming the fundamental ceiling on nanotech isn't too low. Plastination might be disfavored on the grounds that it replaces lipids (old atoms) with plastics (new atoms), but assuming the philosophical attachment is mostly to the proteins you could consider this a viable form of survival as long as the process can be reversed by some kind of sufficiently high grade nanotech.

Fixation in Osmium Tetroxide or something similar could preserve the lipids directly, and might be more along the lines of what the prize competition is doing since plastination is actually something used for art shows, not for electron scanning.