Why do we need identical federal and state laws over us?

[ihopehefails]

I really don't see why we need the federal government to rule over our lives when state laws usually do a pretty good job of maintaining the order of its citizens. Can someone tell me why it is better for the federal government to be the law in our lives when state governments pass and enforce almost identical laws that the federal government does.

 

[lawbuff]

The states ratified the Constitution giving Congress authority to do so, so any blame lies with the Constitutional Convention delegates/signers.

I am though mostly opposed to these two sovereigns trying a person for the same offense, one state, one federal, and it does not violate Double Jeopardy.