to refuse to sponsor a relative who is doing one of those charity holiday excursions for a charity of their choice

[activate]

am torn

we tithe our family income (we set aside 10% we have ongoing child sponsorships plus select specific charities on an annual basis)

a relative is doing one of those pay a holiday charity arranger x thousand pounds to take part in some marathon walk / bike ride and is expecting me to donate

the charity is a religious one and we are atheists - we would not choose a religious charity ever even though they do good

so AIBU

YANBU. A company I used to work for had an annual charity donation budget. One year I sat on the committee deciding which charities to donate to, we immediately ruled out any of these types of 'free holiday' sponsored events for all of the reasons listed here.

Yanbu. It's great to be charitable but it needs to be something that means something to you (you obviously already realise that).
A couple of years ago bil gave everyone in the family goats, chickens, trees etc for Oxfam. It was a lovely thought but I was a bit as personally I wouldn't go out of my way to support Oxfam and as it was a Christmas present thought it would have been nice if it had a bit more meaning to us.
You can't support everything unfortunately.

Pasta - sadly have to agree with you about Cancer Research, albeit for different reasons.

YANBU, there is more than one way to raise money for these trips. asking family to just outright sponsor you is the most unimaginative. Most charities suggest many other ways to fund raise for these trips such as bake sales, smaller sponsored things (like men doing sponsored leg wax etc), jumble sales, raffles etc. If they were doing something like that to raise money for their trip (i.e. actually putting some work and imagination and entertainment value into it) I wouldn't care TOO much about which charity it was for. But if they are just saying "pay money to X so I can go have the experience of a lifetime" then that's different

YANBU.
I would never give to a religious charity. (Or do anything else that may make a religion look good)

Magic - I don't doubt that Oxfam does a great job and manages it's funds responsibly and quite happily support them via buying in their charity shops etc.
Was not at all annoyed to receive charitable Xmas gift, but were I to do something similar, I would make a donation to a charity supported by the recipient, in the same way I might, for instance, ask Dh what aftershave he'd like if I was planning to buy him some as a gift.