I agree with pp that it's this kind of thread that makes me really properly dislike mumsnet. The same with the naked selfies threads.
Huge amounts of money have been raised, along with awareness. That can't be a bad thing.
I think it's really disgusting to accuse participants of being only in it for attention/ego stroking. Everyone to a man who I know, who has done it, has donated (only a couple missed the point and donated to Macmillan or another charity, and at least they donated). I did it, dh did it, as did ds1. We donated to MND Australia. Ds2 didn't want to do the bucket challenge, but chose to donate. All good. It was four donations to that charity, which otherwise wouldn't have been received (as MND/ALS has never particularly come to my attention before).
I was particularly upset with the nasty sneering and snobbery surrounding the naked selfies drive, because as a current sufferer of stage 2b grade 3 breast cancer, over fifty of my Facebook friends donated, and selfied in my name and it was really touching and emotional. To see my friends' efforts looked down on as purely attention grabbing and wankish was hurtful.
If you don't want to do it, then don't, but leave off the people who are donating to a worthy cause and raising awareness, and daring to have a bit of a laugh while doing so.