How Mario got into trouble for people thinking that bricks have a soul.
Perhaps the signature ability of Nintendo's marketable manual labor mascot Mario is his extraordinary jumping capability. He's being doing it to cross gaps, stomp enemies or smash blocks across screens for generations, but since a few years, he's had to deal with a nasty rumor: Could the blocks he's destroying without a care actually be transformed Toads?
A plumber's dirty secret
The main point of evidence substantiating this theory is the second page of the North American manual of the original Super Mario Bros. (1985). Since video games back then usually lacked any intro cinematics, their plot was conveyed in written form, as is the case here.
As part of the game's plot description, it is mentioned that the friendly Toads "were turned into mere stones, bricks and even field horse-hair plants" (the latter referring to those tall bushes you see in the background of some levels). While they can turn back with the help of Princess Peach, doing so would obviously be somewhat difficult if Mario destroyed said "bricks" beforehand. The fan theory then argues that the powered-up protagonist is effectively murdering the kind mushroom people by jumping against the brick blocks they were turned into.
While the exact source of this theory is hard to determine, it was certainly popularized by the video "Game Theory: Why Mario is Mental, Part 2", uploaded to YouTube channel The Game Theorists in October 2013. The video has accumulated over 12 million views since.
A fine distinction
However, in putting forth this argument, The Game Theorists neglected to mention that the line from the manual may not actually be referring to the types of brick blocks Mario can destroy by jumping against.
By turning a few more pages, readers may find a clarification of the Toads' transformations: It seems you can recognize whether a brick block is just a normal brick or a transformed Toad by whether a Power-Up is ejected out of it afterward. Importantly: Blocks that contain Power-Ups (like the famous ? Blocks or Hidden Blocks, for example) are not destroyed, instead turning into Empty Blocks when jumped against.
It seems Mario is doing quite the opposite of killing them, considering the transformed Toads are said to "reward" him for his discovery by handing out the Power-Ups of their own volition.
With the "murder" part of the theory out the way, it's finally also worthy to mention Nintendo seems to have moved past any blocks or items being transformed Toads by this point. Even Mario games that don't feature Bowser and his Koopa Troop, their supposed magic or any Toads still include ? Blocks, smashable Brick Blocks and Power-Ups (for example, Super Mario Land (1989)), so our final advice is:
Just continue to enjoy the games as before; if you desperately need moral dilemmas in your 2D platformers, direct your empathy at the hundreds of Goombas and Koopa Troopas Mario purposefully stomped on instead.