I did, and for the life of me I can't find the part that allows it. It is a given that unless otherwise stated a simple majority is all that's needed to pass a law or accomplish an act. That's why only a majority vote in the House is needed to impeach someone but a supermajority is needed to remove them from office, because the Constitution specifies the 2/3rds vote for removal by the Senate but is silent on what is required by the House.
Now, perhaps you might like to reread the Constitution for your self and point out where the Constitution allows what you say it allows?
There is nothing in the Constitution preventing this Provision in a Law. The Provision wouldn’t apply to all laws just to the specific law. When the Fair Tax is implemented it will have a provision that requires the rescinding of all other tax laws and 2/3 vote.