Let me rephrase that. I 100% totally approve of donating your time, energy and labour. But donating money? The thing about money is that it's "made round to go round", and that it's totally fungible - which is the basis of the market economy - so whoever gets their hands on it can do whatever they like with it. The problem with giving money to an established charity is, to become an established anything in the World-As-Is, an organisation must do some kind of deal with The Prince Of This World (schmoozing big corporates and governments, etc). No matter its mission statements and "good works" on the ground, the larger the organisation, the more embedded it is in the very thing that the act of charity is supposed to be dissolving.
Of course, I'm not discounting the "metaphysical principle" that freely donating something which does have value to the individual is an act of selflessness which is good in itself - but as a consequentialist good, I would really recommend you get into volunteer labour. (And if you have more money than time and energy? Quit your job, schmuck.)