Yabu and yanbu. First up, if you disagree, don't donate- you're under no obligation. If you haven't heard of the charity before your friend/relative/colleague flagged it up and you would like then to donate, well just donate without sponsoring, that's easy enough to do! For example, I did not like the no make up selfie business at ALL and I'm bit mad on cruk but the endless deluge of selfies prompted me to donate to Marie Curie, so it did good in raising awareness.
I don't think charities would offer these events if the charities felt they were not good money raisers.
On the other hand, if it's a jolly then yes, it would be better if somebody paid for themselves if they could. I did a skydive and paid all costs myself, but still asked for sponsorship for a charity and raised money because I thought I may as well- without that sponsorship on my mind and the thought the money would do some good I'm pretty sure I'd have bottled the whole thing. I wouldn't have expected others to fund the jump itself though, no. On the day I went people were jumping for spina biffida, Tommy's, Bliss and War Child amongst others and has they not jumped then the charities wouldn't have made those ££ and I think all those who jumped that day did so with the very best of intentions and for very personal reasons.
I think that if you've done charitable deeds or made charitable donations then by all means be critical when others seem to do them only if there's a benefit to them. On the other hand, if you don't give or haven't ever raised anything yourself then why be down on and sniffy about those with the get up and go to do something?
Finally, for me the biggest issue is that charities have to exist at all. It's far more sickening to me that children's hospices (for example) need charitable donations than it is that some people trek the inca trail and raise a few £££ at the same time.