On the one hand I do believe that we have a certain responsibility as the dominant species on this planet to take care of it. On the other, we are directly affected by degradation of the environment. Obviously through climate change, but also through loss of biodiversity (potentially relevant biochemicals that we never get a chance to study), loss of ground water, loss of fertile land, etc.
I personally find it rather unlikely that a crop failing would cause catastrophic famine in first world countries. We are actually far more diverse with the types of crops we grow compared to our ancestors. Yes, you always hear about loosing heirloom varieties. But for the most part, none of these were ever a staple. On the other hand, we now have access to every major staple crop throughout history. Rice, barley, wheat, corn, potatoes, etc. Add on top of that our improvements in science which allow us to directly combat the potential causes of such a catastrophe in the first place.
Something like what you described would definitely be an abrupt shift in our diets. But it would not likely lead to starvation in fully developed countries. Now those countries already facing food insecurities on the other hand, they would likely be in massive trouble...
