So, to be clear, your arguments are thus:
(1) "Nobody but a "trusted," official representative of the government, or those authorized by that government, should be allowed to defend you or your fellow citizens in an effective manner."
(2) "You and your fellow citizens are all completely incapable of rational thought and behaving in a reasonable and responsible manner."
(3) "Official representatives of the government are always completely capable of rational thought and behaving in a reasonable and responsible manner."
(4) "You and your fellow citizens will never have a need to defend themselves from the actions of an official representative of the government."
(5) "You are incapable of divining, through research, rational thought, and a basic understanding of many of the common political and societal concepts in play at the time, the most likely intent of a basic, well-covered, and openly public right granted to all citizens of the country in which you are obviously a citizen."
(6) "Speed and scope are all that it takes to turn an abstract concept into a completely different abstract concept."
Now, I may have missed one or more of your key points, like "You should have really previewed your post before hitting the Submit button," but I think I got them all.
For (1) through (4), the response is fairly simple: The second amendment expilicitly allows the citizenry the tools most capable of providing the ability to defend themselves from any attacker, regardless of who the attacker represents. This implicitly includes agents of our own government in that list of "attackers," whether that inclusion scares the crap out of you or not. Whether you feel comfortable about it or not. That hypothetical guy having the bad day will just have to be extremely careful about how he goes about declaring just how bad his day was to his fellow passengers lest they feel the need to defend themselves and those around them. If you want to be the one to not defend yourself when the guy decides to start bludgeoning you the head with his laptop because his spreadsheet app decided to crash on him, then be my guest. But, to determine, on your own, based solely on the fear of a potential worst-case scenario, that nobody should be allowed to do the thing you obviously don't want to do? That doesn't sound much like being a responsible citizen to me.
As for (5), you have no idea what I know, how I know it, or where I got my information. You definitely don't know my overall thought processes or my ability to convert concrete ideas into abstract ones and use those abstracts in dealing with concrete situations. Add this to a willingness to actually look for the why of a thing instead of stopping as soon as I find the thing itself (or worse, someone giving me the what), and I often get told I have a pretty good grasp on the motivations behind things.
Now for (6). To reiterate, the only difference between Slashdot and a town hall meeting or a mailed letter or even a community bulletin board (the kind with pieces of paper) is the number of people that can be communicated with and the speed of the communication. There is nothing new to putting words (writing/typing) on a medium (paper/web form) and sending it to a destination (posting board/website) where other people can read it and/or respond to it in a similar manner. The difference between mailing a letter to someone and emailing the same letter is the term "electronic" (electronic + mail = e-mail). The only real difference in these cases being the number of people who can read/post, and the speed at which the messages reach their destination. In this way, saying that the the concepts of writing a letter and writing an email (or posing a message on Slashdot and sticking a note on a posting board) are completely different just show that you pay no attention to what you're doing, and more attention to what you're using while you do it.