Oh yeah, the show was critical of prisons from day one. Although it definitely became a lot more critical from seasons 4-6, his criticism that "it reached a point where people outside of the prison were the crazy ones and the convicts were the virtuous ones" doesn't really make sense to me, because even in its later seasons this show has never shied away from the fact that so many of these prisoners are bad people and/or have done bad thing. Like when they were torturing the guards in season 5, it's not like the writers were expecting the audience to cheer the prisoners on or anything.

Season four was the best season for me because it did have a heavy focus on social justice, but it did so without sacrificing the characters or the story. It all felt like the natural, logical progression of everything that had happened so far. (God, I could write a whole novel on why I think season 4 is one of the best seasons in TV history. It's so hard not to ramble.)

Season 5 felt a lot weaker to me because some of the characters started to feel like a vehicle for the writers to make their point, rather than real people in their own right. The writing started to feel a lot more heavy-handed in this season, which is frustrating because the riot storyline was when the show really needed to stick the landing, in terms of cementing its legacy. (It's like if The Wire dropped the ball during the school-kids storyline, or if the Breaking Bad writers mishandled the end of the Gus storyline.) I thought season six was really good though, and hopefully they stick the landing for season 7. (I'm hoping they flip the flashback structure around and start showing flash-forwards of each of the main characters getting out of prison.)