Why, so that a thriving black-market in deer rifles will develop?

Gimme a break. These so-called "assault weapons" are no more dangerous than an ordinary deer rifle, many of them use actions based upon hunting rifles! "Assault weapons" also fire intermediate-power cartridges; your grandpa's 30-06 Springfield or Garand from WW2 is MUCH more powerful. I am not going to get into technology here, because as a Citizen, I have the unalienable, Constitutional, Human, and Civil right to own whatever weapons and arms I wish, for the defense of my Life and Liberty. "Assault weapons?" You betcha. Machine guns? Yup. 105mm Recoilless Rifle? Expensive, but yes. Tanks? I know a guy in North Carolina who owns three of 'em; takes the things to airshows. These weapons are his, mine, and believe it or not, yours, by Right.
What part of "Shall not be infringed" do you people NOT understand?!

The 2nd Amendment references a "militia." Very well; what is the Militia? According to letters and speeches from the Founders, it is "the whole body of the people." The Militia Act further defined the Militia as all persons eligible for service in time of war; at the time, Males from the ages of 17-45. In the modern context, this may be extrapolated to include women and older people as well. The Militia Act was revised in 1913, with the creation of the National Gaurd, and now specifies that there is a branch of the state Militia which is NOT the National Gaurd or Reserves, called the Unorganized Militia, of which ALL eligible persons are a member.
Therefore, you and I are members of the Unorganized Militia. As such, it is our duty to provision ourselves with appropriate tools, food, equipment, transport, and weapons. Just because you can't/won't do YOUR duty, don't prevent me from doing MINE, if you please.
You will doubtless point out the phrase "well-regulated." Newsflash: 'well-regulated' does NOT mean "state-controlled" in any sense of the term, as it is used in the text of the 2nd Amendment. The term 'regulated' meant then, and still means now, in certain circles, 'properly functioning' or 'in good working order.' A clock with "regulated" stamped on its backface has been tested and found to give proper and accurate time. A rifle that has been "regulated" has been tested and proven to function as desired with a certain charge and weight of projectile. In the 1790s, the phrase "A well-regulated Militia" meant "A Militia functioning in proper order." NOT "A state-controlled military organization."
I am a member of the Unorganized Militia. So are you. I am doing my duty as such. You are not. We have a difference of opinion; well and good, we are Citizens of a Constitutional Republic and can disagree until we are blue in the face. But the MINUTE that you try to abrogate my Rights, which are mine simply by virtue of being Human, you place yourself opposite me.
You want to send ATFE thugs to take my weapons because you don't have the stones to do it yourself. Allright. Try it. Just try. The flames of the war that would start would lick the roof of Heaven before it was done. This ban, thank God, will not pass in all likelihood, because the treasonous scumbags in Congress know what the likely result would be. But if it DOES pass, hang onto something, and pray hard.