> a lot of money (around 50% of income) goes on fundraising
Yes, the Standard Fees for the "charity" Fundraising Industry in the UK and Australia (probably most other countries too) are:
* cash raised: 50%
* direct debits signed up: 100% of the first year's payments
So if a chugger signs you up for monthly donations, and you cancel after 10mths, the charity receives precisely nothing and your intended recipients receive on average less than 15% of that nothing.