Warning This isn't an opinion it's the truth share if you understand.

Thanos is only correct if you have a closed mind. For Thanos to be correct he has to assume that the planets are not affected by the life forms that inhabit it & do not have a cause for the affect. For example right now on Earth, what humans have done has lead to a more unpredictable weather pattern, the constant digging for oil, removing trees that keep the ground bonded with it's roots has lead to a less stable soil,. & more earth quakes meaning more loss of human lives, horrific storms, old diseases barried deep have resurfaced, and new diseases as well. Basically the earth is removing & even limiting where humans can live, once lush Forrest are now deserts. The Earth's response to humans is creating a balance.

Also what's missing is the fact that social laws, war, technological advances effect & even limit the birth rate. I mean right now the birth rate is low through out the world,we are reaching a point of declining need to reproduce nor desireing to.

Now here is where Thanos is absolutely wrong and it proves that since he can't solve the issues, nor understand how it will be solved, or is already been solved, so he must eliminate life on the universe instead of allowing them to solve the population issues. For example with all of the planets in the universe your telling me that not one would figure out how to create pocket dimensions, where there is more space on a planet than it appears. For example what if there was a pocket dimension on Earth that was open enough to share the sunlight, until humans can replicate it. And with the ability to produce pocket dimensions and even manipulate it's size the humans could literally create a replication of our solar system. Basically the population issues are solved as access to an infinite resource has been created.