Is it permissible to donate to Shias in Iraq through charitable organizations, with the possibility that they might use these funds to strengthen their influence over Sunnis?

If the obligatory charity is zakat (definition), then it is not permissible to give it to the Rafidah, and its ruling has been previously explained. As for voluntary charity, it is permissible to give it to a disbeliever, unless it is used to assist in a sin or to harm a Muslim. If the recipient of the charity uses it to harm Muslims, then it is not permissible to give it. It is better to give zakat to those who use it to obey Allah.