Small but important correction. Ron Paul didn't accept the Govt pension. His pension comes from his medical practice years ago. His annuities come from his stock investments. He may command a price for his speaking engagements nowdays, but he worked hard to get to the point where he commands that price.
As far as SS goes, at the time that Dr. Paul paid into that system, it was sold to people as a trust fund for your future retirement. It was voluntary to pay into, not mandatory, and you voluntarily paid it in order to get your money back when you reached retirement age. He was promised a pay off on his original investment into that system, even if it was just recouping his own money. Its a contract he made with the Govt, and there is nothing wrong with requiring the Govt to uphold their end.