What IG said ... and emotions would definitely have run higher in the military than in the civilian population, right through the 1970s, which would have been a formative time for Jack professionally. 'Gamekeeper,' 'Matter of Time,' and 'Evolution' suggest that he operated in theatres where the U.S. and the Soviets were at odds, and a guy in black ops could have racked up a lot of grudges.

I was thinking in terms of what was clearly stated in canon, though, and I definitely get what you're saying -- I'm not sure that line is fully supported. It might even be undermined by 'The Tomb' and 'Watergate.'