By "archaic" do you mean they got there first? Because farming has been around in (e.g.) Arizona for >100 years, and there weren't any problems back then when there was mostly a whole lot of nothin' in the region.
* https://podcasts.apple.com/us/podcast/an-arizona-farmer-on-h...
* https://podcasts.apple.com/us/podcast/understanding-the-real...
Then folks decided that building large population centres in the middle of the desert was a good idea, and here we are.
It should also be noted that Native Americans were also living and farming before white settlers arrived:
* https://en.wikipedia.org/wiki/Phoenix,_Arizona#Early_history
Though it's not like having large civilizations living in a desert is unique to the American (South-)West: see Mesopotamia and Egypt. They're just usually huddle around rivers.
Efficient water usage (e.g. drip irrigation) and not growing comically unsuitable crops like alfalfa would solve this problem, even in the face of climate change.
Its pretty disingenuous to argue the impacts of agriculture today is the same as >100 years ago and act like all the expansion has been the cities.