If you don't require a super majority for general legislation then you end up with back and forth legislation with just a small shift in the majority.

Pass a law this term that will be overturned next term if the vote count shifts a few percent the other way. Not only do we have the filibuster but we have the Veto where the president can require a two thirds majority to pass new laws. Most Governors can do the same thing. The two thirds majority is embedded in our Democracy.

TEK