Thought about what you're saying and you definitely got a point. Sounds really plausible. But (and after watching the end of Thor and the scenes from Avengers including Thanos just again I've found a "but" ;D) actually Thanos never said sth. about weak humans himself. It's always the Other that somewhat tries to convince Thanos to give Loki the scepter for ruling earth and its small inhabitants (and Thanos ruling the whole universe). At the end of Avengers it's the Other again that tells Thanos they were mislead by Loki and dealing with mankind is dealing with death. Thanos still doesn't say anything but smiling. So I'm not really sure if he wasn't aware what mankind is able to do. Of course he wouldn't give the scepter to any guy who comes along so maybe he has seen the possibility that Loki has a chance. But he also should know that Loki has a brother that keeps an eye on Midgard. Of course (and that's why I had to watch the end of Thor1 again) there is a chance that Thor might think that Loki is dead after falling from the bifrist bridge into space. But then he could also imagine that Heimdall will recognize Loki when popping up on earth. So he must have known (or at least gave it the same chance) that Loki could be failing. Or did he even contrive this?
...OMG... the more you think about the crazier it gets
Loki's plan involved the Hulk. He must have known that he can be a threat and therefore needed an army. Is there a chance that Thanos also has knowledge about that "monster" because he screened Loki before (and his "object of desire", too)?
Or is it that easy like you say and he just believed that humans are too weak for a counteraction (without bringing this into question). It's the whole universe he wants to rule after all. He can't afford to just buy a lie. Even if he had Loki shooked like you say, he must have considered that there is a chance that Loki betrays him when having all the power from the tesseract and the scepter.
And if we develop this further... if this really had been such an issue for him, why didn't he learn from that and then made pretty much the same mistake again with Ronan. Is he that gullible? Or just stupid? (We know he isn't.) Is he just so self-confident. Or does he have a plan?
Another thing that doesn't make sense until now is (if it's really true), that Thanos has the empty infinity gauntlet in the midcredits scene from Avengers 2 when saying that he has to do it himself now. We don't know where he got that gauntlet from because last time we've seen it was in Asgard. Maybe a hint that there really is something about Thanos (that he well thought out what happened until now we don't know yet). Or it's just sth. that doesn't fit together 100% in this growing MCU.
