"The Earth's atmosphere is 80% Nitrogen, we don't even breathe Nitrogen, Blight does; as it thrives our air gets less and less Oxygen."
If there's one big "flaw" in this movie it's that I don't think the underlining premise of what's happening on Earth makes any sense.
First of all, if Blight "breathes" Nitrogen then what does it exhale? That exhalant could pose a greater danger to humanity, and all lfie on Earth, than anything else. Though, most of the animal life on this planet exhales Carbon-Dioxide and CO2 doesn't make up a meaningful percentage of our atmosphere -though, granted, plants take that CO2 and makes it into Oxygen.
So if Blight breathes Nitrogen what on the planet is producing more Nitrogen for it to breathe?
We'll go ahead and assume this "Blight" is some-kind of pathogen that somehow came to Earth. Whether the unintended consequences of biological warfare or am extraterrestrial pathogen that arrived via an asteroid or something.
Still, doesn't make a whole lot of sense. As good as Nolan's movies can be, "technical issues" tend to muddy things up a bit. The "microwave reactor" in "Batman Begins" is a problem because it ignores that people's bodies are made up of water and they'd boil along with the water in pipes. And microwaves aren't terribly great, efficient or mostly fast at turning water into steam. Sure, it's how microwave ovens work, but it takes a lot of power and a couple minutes to get a glass of water to reach a boil in a microwave. It'd take incredible levels to get it to turn instantly into steam. Microwaves are also very "directional." The casing of a microwave aided by a fan helps to agitate and deflect the microwaves to ensure some level of complete coverage inside the oven.
"Inception" is a great movie but it suffers from similar technichal problems in that the "dream machine" isn't too fully realized or made to look like it makes sense. An IV to a few people lined to a suitcase and people can... share... dreams? With no connections to the brain?
Same thing here with "Interstellar" which I find to be a fantastic movie but the "Blight" doesn't make much sense when analyzed for more than a moment. It would've made more sense to simply say that the sun was in a period of increased solar activity that was predicted to only grow more and more intense. The solar activity having greatly impacted the climate on Earth meaning a dryer climate and problems with feeding a huge population, only certain crops being able to survive the harsher conditions.