Originally Posted by cherokeesam
Here's my theory on how the Cube works in the MCU. . . .
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.
Does one have to be sufficiently powerful/evil to be able to use it? Algrim is just one of the soldiers, albeit a fairly strong one.
Your theory has merit, though I might modify it to say people susceptible to or influenced by evil use it. Selvig isn't good/then evil/then good, for example.
And maybe, to some extent, the Tesseract is using all these people instead of the other way around.
I don't think any of the "good" people you named have tried to use the Tesseract and failed (whereas lots of people have tried to use Mjolnir and failed, for example). They simply do not make the attempt.
(To pick a nit: the Viking king was not entombed with the Tesseract. The Tesseract actually was in the carving of Yggdrasil, off to the side of where the tomb was. But your point remains valid.)
Another quibble: if the Tesseract is so evil, why leave it on Midgard for 1000 years among all the rubes?