silence is considered a commercial dishonor, and allows the other party to dictate the terms of the contract you're negotiating. Police are excellent contract negotiators ("you are under arrest" is a contract offer, legally), and are trained that if you're not in acceptance with their offers/orders, they pretty much get to do whatever they want to/with you.

Seems the Supreme Court disagrees with your opinion as well [1].

[1] http://www.huffingtonpost.com/2013/06/17/supreme-court-silen...