The M4 is the shoulder rifle of choice by the majority of SWAT teams and military for a reason! The same reasons law abiding civilians should have them. SWAT teams use the M4's because the 5.56 ammunition they use does not overpenetrate sheetrock walls and other barrirer materials in the same way a hollow point 9mm or .40 would! It is a safer round for home defense, a more accurate round, and a rifle should always be your protection firearm because shouldered rifles are more accurate and controllable especially under stress.
Also, civilians should have the ability to protect themselves from government who may steal away thier constitutional rights. protection against overbearing government, protection against armed gangster criminals, protection against drug cartels, protection against those who will murder you or your family without a care!
Americans live on the borders where drug cartels mule dope and illegal goods and tresspass on thier legally owned land. Americans need military style rifles with high capacity magazines to protect thier property and life interests.
May God make smooth the path you follow!