I don't know what happened in later seasons, I only watched the first few. There was torture in the show from Season 1. Jack violently interrogates two people in the first season, later executing one of them at the end of the season. Season 2 opens with a torture scene: http://24.wikia.com/wiki/Interrogation, one of many such scenes in that season.

I don't know how many people here really remember the mood back then. I was just starting college at Georgia Tech when Season 2 of "24" came on. It was hugely popular in my dorm. And the overall sentiment was pretty violent. In the run-up to the Iraq war the next year, it was less controversial to say that we should turn the middle east into a "glass parking lot" than to argue against going to war. And this is of course among people who were relatively liberal compared to the region as a whole.