Yeah, I personally don't like this bundling of fun activities and charity. If you want to run a marathon, run a marathon. If you want to give to charities, just give. Don't make a pretence of charity to do what you find fun.
I agree with the sentiment although lots of people run marathons and raise money for a charity as a motivational aid. I don't see anything wrong with this.
However, if someone wants to do a parachute jump, cycle the Great Wall of China, etc, then yes, they should just shut up and fund it themselves.
I'd be much more willing to support these sorts of events if the participants underwrote the costs themselves.