"What if you prefer not to give to charities which you aren't sure *are* Christian, again due to the leading of the Holy Spirit?"
That is your choice, but I thought we were discussing the concept of cooperation rather than who we personally donate to? For my own part, I have no problem donating to charities regardless of if they are religious or not. If a non-religious group is passing out food to needy people or if they have a job program, I have no problem donating what I can. This, providing that I know my efforts are benefitting those intended.
There are churches I am not fond of, particulary one around here. But I still donate clothing on occasion, because it is about helping people, not my disagreements with the pastor or people in his church.
Good for you.
I personally prefer to give to Christian charities because they are trustworthy to me.