Yes it was torture. Using Tsukuyomi IS torture . Go and read the manga again(since I don't like posting scans) Then there was the hotel torture when Itachi returned to Konoha(when he tortured Sasuke-again for 24 hours!). And yes, he was an idiot since torturing Sasuke was one of the reasons why he became a supervillain. I won't even mention torturing Kakashi for 72 hours(one of Konoha's top jounin). He was also a villain for trying to make Sasuke a puppet via KA.(none of those things are what smart guys or good guys do) Try again.
In normal circumstances yes, I would agree. But you have to pay attention on Itachi's circumstances too. He was with Kisame who didn't know Itachi had left his brother alive. When Sasuke suddenly appeared then only he found it out. Someone like Kisame was not likely to not ask questions if Itachi was going to be nice to him. Not to mention rest of Konoha also needed to see him as a villain or again people would suspect. Secondly and more importantly- Sasuke needed to learn the scope of sharingan to unlock them faster. With the whole clan gone it took Sasuke quite a while to realize he had awakened sharingan. His early progress was not that fast. Itachi showed him how much more he could do with his eyes and how much the gap was. Sasuke was terribly underestimating him at that point.
If you think back Kakshi too gained MS ages ago along with Obito when Rin died. But he didn't realize what he had and if he could use it till Itachi used it on him. Only after being put in tsukoyomi he trained his eye further than just copying other techs or using it to fix his raikiri. Hokage might have made him in charge of only other remaining sharingan but he didn't know that much about it himself to train Sasuke more at the time.
Itachi even then had few options to keep his facade up and still leave hints to Sasuke. He needed to do enough to shut Kisame up and not let others suspect him. Akatsuki back then would have made him toast if his game was known or suspected.
In the end they are all shinobies in a shonnen manga. Itachi was leading ANBU almost around round same age.
You guys make things complicated and always judge the verse in the manga with your own rl ... Sometimes I wonder how come we are not getting threads demanding to know why child labour is not illegal and they are even allowed to go on dangerous missions when they were under 18. :|