I think the trivia entry here sums it up perfectly.

Rating: Null/10 (26 April 2018)

The trivia entry, quoted, is "After the credits 'end crawl' come the words "Thanos will return" - making him the protagonist of this movie."
Never has the IMDB so quaintly and indirectly summed up exactly what is wrong with a film. It is basically the same problem as was with Spiderman Homecoming, and when you know your butt from your ear about anything, just a few minutes of thinking about it will make the problem perfectly obvious to you, too.
The problem, essentially, is that the villain, so-called, talks more sense than any of the so-called heroes put together.
When workers in China have to have incredibly cruel and devious means put in their way to stop them from committing suicide. When hundreds of children in India go missing almost every day. When half of the population in the richest country on Earth regularly experiences food insecurity. These are all moments that a smart person, that is, a person who does not unquestioningly eat up every morsel of the same recipe Marvel is shovelling into theatres every year without complaint, recognises as Thanos being right.
If you are new to this planet and have no idea who Marvel, Thanos, America, China, or India are, here is the freeze-dried version. Thanos is deeply saddened by the fact that he has watched multiple planets die because their dominant species, usually a very Humanoid-looking one, has overbred to the point where instead of the bonanza and excitement that the religionists promise when we all go forth and multiply, the world ends up dying in pain. So he seeks to possess the Infinity Stones, to bring a halt to worlds becoming uninhabitable due to their dominant species overpopulating them, and instead limit the species to a point where both the species and the planet can coexist. If that sounds like horriblebad to you, then congratulations, you are exactly the problem that the real Earth faces. Those of us who know that we might not have diabetes if the world was not so overpopulated (or any of the other debilitating and destructive diseases that have increased manifold as the Human population has quadrupled in less than two hundred years) can accept the reality that if we do not get a Thanos, and soon, nature and this planet is going to do as Thanos does. And if there is one thing that history as well as science can teach even the most naÃ¯ve idiot simpleton, it is that nature can be counted on to be a quintillion times crueller than a quintillion Thanoses put together can ever fool idiots into thinking they are.
Case in point. In the last few months, a bacteria has appeared in a part of Asstralia that, whilst not urban and connected to the rest of the world, is hardly uncivilised, either. This bacteria appears as a boil inside the skin, and generally rots off the flesh in which it appears. If you are lucky, you can lose a huge chunk of fat and muscle to this bacteria. If you are not so lucky, you might have to kiss multiple limbs goodbye. I think it is ironic that a bacteria that can turn a healthy alpha into a quadruple amputee overnight, when choosing which part of the so-called First World to appear in, appears in the one that is on record as being the cruellest in the OECD to its disabled people.
Thanos probably saw something like this happen on the homeworld he tells us during this film was destroyed by overpopulation.
Marvel, can I offer you a suggestion concerning your next lot of films? Other than stop regurgitating the same three-act good guy meets bad guy meets ordained resolution structure, that is? Here it is. Stop demonising the people in your stories who talk sense. Overpopulation is a very real thing, and unless the Human population of the Earth stops growing, starts declining, and soon, the worst of the consequences of overpopulation are going to make flesh-rotting blisters of bacteria seem like a mild "cold" by comparison.
Thanos is the real hero of Infinity War, and a good storyteller would know that.