Who knows, maybe Thanos did everything to save the universe.
With the toy figures of Avengers 4 is leaked, new characters that we may see in the movie was being speculated. Some of these characters were new. Well, we know that Thanos isn’t alone in this new movie.
As you know, Disney has bought Fox but Disney can use characters from Fox after Avengers 4. It is revealed that Marvel bought the rights of one of these characters from Fox, earlier. During the shooting of the first Deadpool movie, Fox wants to increase the power of Negasonic Teenage Warhead and they consult Marvel. In the meantime, Marvel and Fox do an agreement and Marvel lets Fox modify Negasonic’s powers and in return, they take back the rights of Ego, which we have seen in the Guardians of the Galaxy 2. Looks like Marvel didn't get the rights of just one character.
According to a widely spoken theory in Reddit, Leroy Patterson, a strict Marvel fan on Twitter, told Galactus is in this agreement. It is speculated that if the Avengers team can go back in time where Thanos snapped his finger, he would say “I wanted to save everyone from him” as his last words. This person is Galactus. It turns out that Thanos destroyed half of the living things in the universe so Galactus would not attack us.
We don't know if this theory is real or not. But Marvel may have Galactus as a secret and powerful weapon. This can even lead to a new beginning of Marvel movies. Who knows, maybe Thanos did everything to save the universe.