I submit to you that Ben Franklin did not have the slightest concept of either the magnitude or the rapidity of the destruction that modern man can inflict. There was nothing in his frame of reference to compare.
Well, let's test the context. Could he have guessed relative to his time?
In 1790 there were about 4 million Americans, and maybe 500 million world population.
Today we have about 300 million Americans, and 6 billion humans.
So are weapons more destructive per human than they were in his time? I think so. Are we asymptotically approaching some maximum suportable population? Going thataway, but not near there yet.
So that really doesn't answer the question, because I don't think his statement is modified by total population. In fact, I think he would underscore his concerns if he knew for each American in 1790 there would be almost 100 more in 1990 that the government might seek to control. I think the basis for his concern is the inherent danger of consolidating power of "security" in the government, rather than the distributed liberties of the people.
A consolidated government led by Xlinton, for example, can be subverted overnight. Distributed liberty depends on the virtue of an entire populace, which in America has always been vastly weighted toward the good, and in that case almost impossible to subvert.
If the infiltration, decay and dumbing down continues, and the people do not protect their own liberties, then they don't deserve anything, much less a secure state.
And this does not depend on the level of destruction man can command.