The vegan hammer is the incorrect idea that any problem on earth can be solve by going vegan. Are you under weight, over weight, bad knees, heart disease, cancer, global warming, global cooling, world hunger, toe fungus, El Niño, La Niña, all things can be helped by veganism! (according to vegans...)

This goes back to the Law of the instrument, which is that if you have one familiar tool you will become overly reliant on it.
Or in simpler terms "if the only tool you have is a hammer, every problem looks like a nail".

When you eat dirt for the first time and leave your family to build a shack in the woods