Where to start.
First of all, using the term 'assault weapon' or 'assault rifle' is a red flag. This term has been miss-used so much it has lost any meaning. The military doesn't consider the AR-15 a 'assault rifle' because it is only semi auto (i.e. does not have select fire). Some people consider anything scary looking an "Military style assault rifle", use term at your own risk.
Fortunately for all of us, you don't get to dictate what somebody can 'reasonably' have in their house. An AR15 is no more of an 'accident waiting to happen' then any other firearm. The AR15 is a perfectly acceptable home defense weapon, some times more then one bad guy shows up. According to police statistics, one in every three too four rounds hit (here is one of many links discussing it: http://www.nytimes.com/2008/05/08/nyregion/08nypd.html?pagewanted=all&_r=0). Despite what the movies tell you, it typically takes several shots to disable/kill. So, assuming two hits to disable (low according to statistics) + three 'bad guys' = 18 to 24 rounds expended. And these are numbers for people who are required to train and qualify with their weapons. I will gladly take my 30 round standard capacity mags, thank you! Personally, I do prefer a pistol for home defense. I like my .45 "military style assault pistol" for this purpose. It also has "assault clips", FTW!
Lets also not forget that they are many sporting and competetion uses for an AR15.
It also gladdens my heart that the AR15 is currently (and has for quite some time now) been selling in record numbers, by far larger numbers then any other single firearm. Magpul, which makes 30 round (standard capacity) magazines, is well over a million magazines on back order. Last I heard they estimated 3+ million AR15s in the hands of US citizens.
"...one possibility is you expect to fight the military, in which case you are hopelessly outgunned anyway..."
Not really a fan of history are you? Wars have been fought and won by a bunch of out-gunned untrained peasants for centuries.
"The second amendment does not say you have a right to buy the biggest gun ever made just so you can imagine something else was that big, I'm sure if they knew what an effective killing tool firearms would turn into they would've been a bit more restrictive even then."
Our founding fathers were smart men, I am sure (some of them being inventors and tinkerers themselves) that they knew that better weapons would be invented in short order. They didn't put any restrictions on the state of the art in 1787, why would they put any restrictions on future weapons? I am sure glad they didn't.
"The Constitution was never intended to be unalterable, that's why they created a process to allow changes to be made to it, it's only supposed to need a majority vote. And unlike the first amendment, that could realistically happen with the second."
Of course it can be changed, it is very very hard to change the constitution (by design). The US Senate cannot even pass a bill (with few restrictions), how do you expect an amendment (with a much larger % of yes votes) to pass? Pure fantasy.
Bun and bullet registry is a poor idea, for so many reasons. Canada tried it, spend 20 years and hundreds of millions of dollars on it, they are now the process of dismantling it. Their own words: “The Harper Government has always been clear; by eliminating the wasteful and ineffective long-gun registry, we can instead focus our efforts on measures that actually tackle crime and make our streets and communities safe,”. It sounds like they still have a registry for handguns, I am curious how long that lasts.