OP, I do think you have come across as rather smug and judgemental on this thread, which does no good to your cause at all.
Personally, I would not give to Christian Aid, as I choose not to donate to religious charities. That's not to say that these charities don't do a lot of good work, but there are others which do equally good work in the same field, and I prefer to give to those instead.
Having said that, I don't really mind doorstep collectors or chuggers etc, as I realise that charities have to collect their money somehow, and they will do whatever works best. I say good luck to them! Yes, it can be quite irritating if they call at an inconvenient time, but a minor source of irritation for me pales into nothing when compared to the suffering experienced by many of the people that the charities are trying to help.
If I don't want to give to a particular charity, I just say so. I don't really understand why people feel "guilted" into giving. I feel no guilt at all.
I already give a significant amount to my chosen charities each month, and my conscience is clear as I'm doing what I can. I can't give to every worthy cause, and if I had spare money to donate, it would go to one of the carefully selected charities that I already support. If people feel guilty about saying no to a particular charity, perhaps that says more about them than it says about the charity - maybe deep down, they feel that they should be giving more.
OP, at the end of the day, you need to accept that you will get a mixed response when collecting for any charity. People shouldn't be rude, of course, but some people are arses, and if you truly believe in the cause you're collecting for, you will take the rough with the smooth and shrug it off - the cause is more important than how you feel on other people's doorsteps.