I am glad you got to the arguments instead of going after the actions of the gun control folks.
My thoughts are that we need to make it harder for the "nuts" to get guns, but there was no indication this guy would have been seen as "nuts". 
We agree on he alerts for such large purchases. That is a starting point. 
We disagree that there are legitimate reasons for such purchases (except for a gun collector). Gun collectors could pay a large fee (since they can afford many guns) and that money used to pay for regular checks of their activities. 
You justify a "security force" because some people feel a need to protect their wealth. I disagree. How many people feel that need? I am for something that is a pervasive need, but not if there are just a few. Is that need rational when there are banks to keep stuff, alarms and safes? 
Your defense of keeping an arsenal is that it is justified if people feel a need. But who makes that call? Anyone who feels a need for an arsenal?