Federal flag no State Flag is that what you are saying?
I think one flag is enough, because it signifies a unified country. Divided countries have lot of unnecessary turmoil.
The old glory is a symbol of UNITED States.
If a state wants to fly their individual flag on a state building, it should have a secondary status. Such as inside the building or on a lower level. All federal buildings which includes post offices should only display the national flag.
That is how I feel.