The Infinity Stones/Gems are depicted as being amoral, fundamental aspects of nature that can be wielded for either good or ill.
The power over the “soul” is described as being special but no where in Red Skulls monolog does it speak of said power being “good” or “for good”.
The test of character was about one’s dedication to whatever it was they wanted to wield that power for, such as for evil as was the case with Thanos, or good with Hawkeye/Widow.
In a way, what it was testing was, like I said, the line between dedication and obsession, and if the person who wanted the artifact was willing to throw something away that was nearest and dearest to their own soul.
I actually like the “the powerful maguffen doesn’t give a damn about good or evil” aspect. Power is power, it’s all in how one wields it.
A common refrain throughout both movies was the line between duty and zealotry, dedication and obsession, “I can do this all day” vs “I am inevitable”.
In that light, the sacrifice for the soul stone works beautifully. In my opinion.