Avengers: Endgame is a month and many days away so it's no surprise to know that fan theories are ramping up to the max. This isn't a huge problem since fan speculation has always been a big part of any fandom and it can lead to some fun discussions. However, this fan theory is fairly intriguing since it would make a ton of sense and lead to something really tragic.
This theory on Reddit brings up a scene from 2014's Guardians of the Galaxy where The Collector is discussing the lore of the Infinity Stones. He mentions how a group of "extraordinary beings" were able to harness the power of these stones for a moment before they were overpowered and soon destroyed.
During the end of Guardians, it takes Star-Lord and his whole crew to hold one stone and survive so having each member of The Avengers carry a stone could lead to disaster. Star-Lord is technically dead too so he can't warn them about this, though Rocket technically can. We know some Avengers will survive but it's clear that not all of them will *cough* Iron Man *cough* Captain America *cough.*
Avengers: Endgame comes out on April 26. Fans will want to check out Captain Marvel later this week before Endgame since that film will probably have huge implications for it.