And that's exactly why I'm against donating to cancer research.

I think opposition to donating to cancer research (as opposed to donating to more cost efficient options) is obvious and accepted (here). Still, I'm selfish enough that if I had cancer I would treat it, which is what was actually being considered/compared to cryonics.

I'm sure this has come up before, but I think there are some cases in which cancer research donations make sense. Often donations geared towards the curing of specific diseases is prompted by some personal emotional connection to the disease (e.g., someone in one's family suffered or died as a result of it), and I expect these kind of emotional donations don't replace other would-be-efficient charity donations but instead replace general spending or saving. That said, I don't actually know if that's the case.