Fans of the Marvel Cinematic Universe are still trying to figure out what they just saw in Infinity War. There's a lot to take in, which leads to multiple visits to the theater to try and unpack everything that the Russo Brothers put into the movie. After a few viewings, certain things become more clear and speculation begins. Before you know it, there's a fan theory that suggests that Loki is the true villain in Infinity War, not Thanos like everybody else believes. There are major SPOILERS for Infinity War and the MCU in general below, so read ahead at your own risk.
Loki is responsible for a lot of havoc that occurred early on in the MCU and the safety of the cosmos was definitely compromised by a few of his deeds. Just in the very first Thor movie, Loki gets his brother banished to Earth and then tries to kill him with a giant robot. Additionally, he starts trouble with Frost Giants, and then later destroys the Bifrost Bridge. This all happens in one movie. It ends with Loki traveling through space to make a pact with Thanos to retrieve the Tesseract, which leads us to the first Avengers movie where Loki makes Earth a living hell.
At the end of the Avengers, Thor brings Loki and the Tesseract back to Asgard. In Thor: The Dark World, Loki banishes Odin to Earth and then impersonates him for a number of years, all while Thanos is easily able to put a plan in place to obtain the Infinity Stones. Thanos' trip to Nidavellir would have certainly been spotted under Odin's rule. Heimdall would've easily been able to stop the Mad Titan from getting the Infinity Gauntlet made, but Loki pretending to be Odin had Heimdall replaced with Skurge.
Basically, Loki is responsible for Asgard not guarding the cosmos for quite a while, allowing for some bad stuff to go down. Thanos was able to gather everything he needed to get all of the Infinity Stones thanks to Loki's carelessness, therefore making him the very reason behind Infinity War. It's a pretty decent argument that Loki is the true villain in Infinity War and pretty much the entire MCU. Even in death, Loki still screwed the Avengers and the universe over.
The Tesseract could have been destroyed on Asgard had Loki left it there instead of bringing it on board the refugee ship. In all seriousness, Loki simply helped the process of Infinity War along. He went out trying to stab Thanos, which was a noble deed, but it was a little too late. Even the Hulk was no match for Thanos at that point. As for his death, we'll have to wait and see if it sticks when Avengers 4 is released next year. But for now, it certainly seems that Loki is gone for good. You can read more about this theory at Buzzfeed.