Here's my theory on how the Cube works in the MCU. I *think* this is what Marvel Studios intended, because I find there to be too many coincidences otherwise. Check this out:
In the MCU, who have we seen activate the Cube, successfully or no, to at least some degree? Answers:
Selvig (when he's possessed by Loki)
Hawkeye (when he's possessed by Loki)
in theory, Thanos (since he tasked Loki with bringing it to him, and since it's always been iconically associated with the character, along with the Gauntlet)
And who *hasn't* been able to, or hasn't tried, to activate the Cube while it was in their possession?
An unnamed Viking king, who was entombed with the Cube in Norway (beginning of CATFA)
Thor (carries it in a case back to Asgard at the end of Avengers)
Selvig (when he *wasn't* possessed by Loki), and all the scientists at the JDEM lab at the start of Avengers
Odin, in theory: In CATFA, Red Skull hints that the Cube would be the "jewel in Odin's Treasury" --- so why doesn't Odin seem to use its power himself?
A quick glance at that list tells us what?
That only evil people can manipulate the Cube.
Ergo: the Tesseract is, itself, an evil object.
That would explain how/why Odin hasn't just used it to wish all the bad stuff away, and why Algrim would be able to activate it.
THE COTTON AVENGERS
...They move like slick cotton on oil.