When Warren talked about Congressional reluctance to tax the rich, he said that it was time to raise taxes on the rich's income. Specifically, he sees the need to balance the budget on the backs of young entrepreneurs that are earning current income, not on their wealth.
In the above article, his father talked about the same income tax over 50 years ago. He warned about the loss of liberty when government trades off individual liberty with security; " In that event you have traded the reality of liberty for the promise of security."
Warren is expressing the same logic his father had expressed, only Warren is in a different position. He knows that in order for him to maintain the huge accumulation of his wealth, it must be secured by the solvency of the US government.
If Warren Buffet had expressed the need for higher taxes across the board, he would have threatened his own wealth. He's just acting on the combination of those "inherited instincts" and the animal instincts to remain as "king of the hill".
Warren has directed a large portion of his wealth to charity, which is a great statement and he now wants to protect that legacy far into the future and deprive the younger generation from competing on a level playing field.