Rav Yehonoson Eibushitz says that The Yezter Hara's main ploy is to confuse us and blur the lines between good and bad. If he can manage to get us to sin yet think it is the right thing he has scored a major victory because this paves the way for a lifetime of aveira. If he cannot manage to convince us that the bad deed he wants us to do is bad and we clearly see the truth his next last resort is to persuade us that although it is an aveira we can always give money to a good cause that will absolve us and somehow wash away our aveiros.
This is what the Navi tells in the Haftorah of Shabbos Shuva "V'Lo Yoimar Eloikeinu L'Maasei Yadeinu"; we will no longer say to Hashem let our hard earned money that we gave to tzedoka be our kapara.
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