Sure Pakistan may have been a dangerous place in 1981. However, the BC Truthers are not saying that Obama visited a dangerous place in 1981. Instead, they are saying that Obama visited Pakistan when it was against the law for Americans to go there.
Why not just say "Obama visited a dangerous country in 1981?"
Why is it they are stating an outright lie regarding the legality of travel to Pakistan in 1981?
Your words, not theirs. They are saying things like "prohibited" or "restricted". It's quite possible, although I do not know, that Pakistan would not issue visas for "tourist" visits, but would allow "business" travel, or would allow "official" travel, but not "private" travel. I'm pretty sure there were at least travel warnings for Pakistan back then, as there is today or advisories/alerts as there is now for India