Odd that they only did this with the second amendment, huh?
They didn't do that for religion. Or free speech. Or a free press. Or freedom of assembly. The right to petition. The right to a jury trial. The right to be free from unreasonable searches.
They didn't want to achieve those goals?
"then when need arose to call up the militia there would then be no assurance that enough respondents would actually have arms."
The Militia didn't show up with arms when called to the War of 1812 -- and it wasn't because the feds disarmed them.
Sure they did. But due to a lack of enterprise for the war and inept leadership in the active military, it didn't work very well. You can't rule over militia like British Lords and expect them to fight for you.
Read a book will you?
Try again to describe an "arm" that isn't suitable for the "militia".