You obviously do not understand the term sin...whether you think so or not, the same laws apply to you as everyone else.
If you think not, then drop a book and it should float. Stick your head under water and breathe. Fly from here to Hawaii with your arms. Do not ever eat or drink again, and tell me how long you live. Just because you do not understand a law, does not truly mean it does not apply to you as well.
Break a federal law, if you go to trial, just let the judge know you broke no law because laws don't apply to atheists and agnostics, he'll let you go...after all, ignorance of the law excuses you...right?