Is it important when I buy a wooden table that I'm given full details of how it was made, how the pieces fit together, what glue was used, what size router bits, etc?
Now the species of the tree your table's wood was taken confers it with quite distinct qualities and, some would dare to say, "personality". The particular process used to assemble it may or may not imbue it with additional properties by performing (potentially nefarious) rituals. Ditto for the different substances that may be used as glue. The router bits may have magic properties themselves, even if the table is otherwise ordinarily Muggle-made.
The problem is not that all this could happen. The problem is your mental model of a wooden table is so dissimilar to reality that you have no way of making informed decisions on what piece of furniture to bring into your home/life.
What if you wanted your wooden table to be two inches shorter? Should you be both technologically and legally prevented from sawing two inches off each of the legs?
What if you wanted to build your own wooden table? Maybe you don't need the original schematics, but should you be both technologically and legally prevented from examining your own table to learn how it was constructed?
What if (for whatever perverse reason) your wooden table did in fact come pre-installed with a miniature surveillance camera that sent footage of you back to the manufacturer. Should you be both technologically and legally prevented from removing such a device from your table?
The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this.
Sure, you can reverse engineer a piece of software. But that's working around an obstacle. The point of free software is that there are no obstacles which would impair your ability to inspect, modify and change it in any way you see fit.
Also, I believe that most EULAs for non-free software have clauses which specifically forbid any attempt to reverse engineer it. I could be wrong, of course, but I doubt it.
You miss the point of what software freedom is supposed to be about -- it is supposed to give everyone the same ability to understand and modify the software that the original author has. The source code is almost always the most convenient and preferred form of software for authors to read and edit, so it follows that to have the same freedom they do, you should be able to read and edit the source code.
"Is it important when I buy a wooden table that I'm given full details of how it was made"
A perfect demonstration of why "open source" is problematic. Stallman doesn't care especially about open source as the way things are made. He cares about freedom. If you can use your table freely how you like, great. Software happens to require access to source to preserve that freedom. Whether it was written using open-source methods is irrelevant to Free Software.
Again, this is a misunderstanding. There should be a Free Software Ideology 101 FAQ or something; probably there is but I don't have a link. Stallman doesn't care about your wooden table. However, you might care if when you decide to cut the table in half and put in an extra board to extend or replace the table legs, the government swoops in with army of patent attorneys or wood gestapos to prevent you from having your way with your own table.
Now the species of the tree your table's wood was taken confers it with quite distinct qualities and, some would dare to say, "personality". The particular process used to assemble it may or may not imbue it with additional properties by performing (potentially nefarious) rituals. Ditto for the different substances that may be used as glue. The router bits may have magic properties themselves, even if the table is otherwise ordinarily Muggle-made.
The problem is not that all this could happen. The problem is your mental model of a wooden table is so dissimilar to reality that you have no way of making informed decisions on what piece of furniture to bring into your home/life.