FSS, do yourself a favor and refrain from telling people what you think they experienced first hand. I was there. I know what I was told. You were not.
Second, this interview took place during the cold war. Yes, things have probably changed since then.
Third, the job did involve significant work overseas in those very countries you cited. One's ability to "fraternize" (that was the word they used) was limited. Again, things could have changed since then. My point is to show where some of these concerns have been and what such clearances could be like.
Fourth, I live not far from a place that has some of most secret squirrel stuff in the US (Fort Meade, Maryland). I know quite a few who have worked or still work there. I know many who have very significant clearances. For most, things go wonderfully well --until perhaps one day, they don't. Navigating through the maze of security clearances is great until the paper-work goes awry or until you annoy some arrogant muckety muck with too much authority for his or her own good. I have seen this happen to several individuals I have known.
I speak from the personal experience of having been there, and from personally knowing many who have had these clearances as well.
Working with a clearance is often difficult and frustrating because, even though you're cleared, the sources of information are frequently obscured. Often there are clues that the information may be wrong, but you have no way to call someone up and say "Could you please re-check that information because I have a concern that it may be misinterpreted?"
Again, Security clearances are not to be taken lightly. Admittedly, if you want to design weaponry, there really isn't much choice but to get one. However, exoskeletons, aircraft, and batteries (the sorts of things the original post mentioned) are not necessarily military hardware. There are civilian sides to this too, and you may find that it is more fun working in a profession where you can share ideas freely.