"I would do anything for love, but I wont do that" is not an internally consistent message. It doesn't make sense. Either he would do anything for love including that, which could be simplified down to he would do anything for love. Or, he would do almost anything for love except that, which could be rephrased to that is the only exception to what he would do for love. It can't be both at the same time unless he wants to be illogical, in which case, words have no meaning. They just become sounds. While the song is topically about him defining what he would or wouldn't do for love, the deeper meaning is his struggle to decide whether to live in reality or go deranged. He was really going through it. No wonder he wrote a song that musically depicts despair. Poor guy. 
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"Am I wrong?" - Walter Sobchak