I think that is in part that a lot of people don't understand the significance of what has just occurred. Even now there are people in government who are 'alarmed' that a private company has this capability. After all, its a technology we're attempting to deny the North Koreans and now Elon Musk's company has all of the parts it needs to build an intercontinental weapons delivery system. The Dragon capsule can be 6 tons. Even neophyte nuclear weapon designers could probably make a device that is less than 6 tons. What is worse is the company won't just die a horrible death if our government pulls all of its contracts.
So where does that leave us? In a very very interesting spot. We are approaching a point where orbital launch technology will be available to 'everyone' and we have to deal with everyone having it. If you were around for the 'great super computer panic' that was when our government realized that there were no microprocessors they could constrain from export that would allow bad guys to build their own super computer using clustering techniques.
Its a similar problem but with the twist of being actionable (or being able to exploit it against the national interests of the US more easily)
Its also one of the reasons I've been following the progress of SpaceX trying to build their own launch facility in Texas. You might see how that combination (private space craft company + private launch facility) would exacerbate the problems for people who wish to keep this particular genie contained as long as possible.
I must admit I haven't thought about what the privatization of space (and SpaceX specifically) means regarding weaponization and proliferation. I suppose I always figured the main thing restricting proliferation is engineering the payload and not the delivery system. I guess that's only true for nuclear proliferation, though.
It's harder. Early space program rockets were all souped-up ICBMs, including the R7/Semiorka (Sputnik and Voskhod rocket) Redstone (Mercury rocket) and Atlas (Gemini rocket).
If you can put something into a pre-chosen orbit you've got the launch and navigation down (after all an ICBM in in 'orbit' that just happens to be highly elliptical and intersects the planet rather than goes around it.) But there is always the mass problem, conventional bombs, combined with relative lack of orbital precision, means that even a 2,000 lb bomb which is a 'big' iron bomb if you can't accurately get it within a mile or two of its target it won't be very effective. A nuclear weapon clearly can 'miss' by a couple of miles and still be very effective, but they are really really heavy unless you know what you are doing. The first bombs built by the US weighed in about 5 tons, but they did damage equivalent to more than 20,000 tons of explosive (a 'gain' of 4000). State of the art weapons have much higher yields. But if you're new at the game you have to have a rocket that can lift 5 - 6 tons before you are a 'threat' to the rest of the world.
"I suppose I always figured the main thing restricting proliferation is engineering the payload and not the delivery system."
Well if you can build a bomb, but the only way to hit someone with it is to fly it in on a huge transport plane, or drive in with it on a truck, it is both easy to defend against and you have plenty of time to figure out if you need to defend against it. If on the other hand you can launch it into space and have it fall out of the sky some where in 45 minutes to an hour, that requires a different strategy on the part of folks you might seek to attack.