Very true. I had a friend convicted (he was sentenced Tuesday) for having a short rifle in violation of NFA. This came even though, in court, it was proven the gun was made before the NFA went into effect and it was supposedly therefore exempt. It was his military survival rifle, he was special ops and it was given to him on his retirement after 34 years service.
Don't say "they can't do that". They did do that.
Be careful out there.