The first 10 Amendments were second thoughts. They were put in to reinforce the notion that blessings (i.e., rights) bestowed on the people by God are not to be taken away by the government. This is implicit in the articles of the U.S. Constitution, but some founders felt a need to give it explicit expression.

So the Bill of Rights is not technically necessary, since everything flows from the premise of people processing unalienable rights.