Obama is not nearly so good as you think. He has lied (a lot) over the course of his career, and his politics are best described as center-right or far-right. Guantanamo Bay is getting worse, he's stepping up the war in Afghanistan (where our "ally" is a brutal, fundamentalist, misogynistic regime) and the list goes on and on. I could continue, going in depth on his policies towards homosexuals, suspects' rights, big business, labor, et cetera, but I think you get the idea.
He is only a leftist from the bizarre American viewpoint, and that viewpoint is a complex product of myriad social factors, most notable of which is the fact that whoever is the lefter candidate is assumed to be a leftist.
From your link He stressed the mistreatment did not appear to be directed from above, but was an initiative undertaken by frustrated U.S. army and navy jailers on the ground.
As for Afghanistan, price of doing business, do you propose fighting the Taliban there without propping up the regime ?. In foreign policy national interests always trump civil rights. Always has, always will.