I think I know the reason for this. Gene Roddenberry was a WW2 veteran i.e. the Geneva Conventions had a personal relevance to him. In the wars of the past you had to assume that many of your own guys would be captured by the enemy.. and that you might end up being one of them. In that scenario a strong international condemnation of torture suddenly looks way more appealing. In contrast, America's modern "wars" (I do not think these one-sided affairs deserve that name) do not lead to a noticeable number of American POWs. And you no longer have to worry about being drafted yourself either.
I think the foundation of the acceptance of torture in contemporary America is the firm conviction of the supporters that they will never be at the receiving end.
This type of thinking is unfortunately widespread among humans everywhere. It is never moral and often unwise to support a system you would not support if you did not have a favorable position within it.