Dumb machines- why not just poison gas the planet?

This was already touched by the Red Letter Media, in their .. was it Genisys or the other crap movie review.

You're right, of course, but that's not the ONLY illogical and nonsensical thing about this movie - if you read my posts, you can realize almost NOTHING makes any sense in this movie.. from the coffee to the hydraulic press.

Not to mention ENORMOUS BODYBUILDER type Austrian-accented killer robots that have BAD BREATH.

I mean, no one would _EVER_ believe someone to be human unless they have bad breath, right? It's ESSENTIAL ENOUGH that Skynet not only designs and plans for these MASSIVE infiltrator robots to have bad breath, but also tests and implements it.

Why would Skynet even know what bad breath is, why waste time with this kind of minutia? It's not like it's essential for computers to learn how to SMELL..

I'm not sure what planet the Terminators were coming from but maybe on their planet they didn't know about what poisons might kill the people of Earth.