I already said this in a different comment, but the difference is that we were not designed while a Swiss army knife was. Design implies intent— it implies that something was developed for a purpose, that it's supposed to be used in a certain way.
Whether or not I use the corkscrew on my Swiss army knife doesn't change the fact that someone built the corkscrew for the purpose of opening corked bottles.
The enzymes/features humans possess that enable us to consume meat were selected for because at some point in the history of our species they enabled our ancestors to survive while others without the related genes did not.
This can change at any point, for any species. If we are no longer in an environment where eating meat confers a significant survival advantage then the fact that we evolved to be able to eat meat has absolutely no bearing on whether or not we should.
Whether or not I use the corkscrew on my Swiss army knife doesn't change the fact that someone built the corkscrew for the purpose of opening corked bottles.
The enzymes/features humans possess that enable us to consume meat were selected for because at some point in the history of our species they enabled our ancestors to survive while others without the related genes did not.
This can change at any point, for any species. If we are no longer in an environment where eating meat confers a significant survival advantage then the fact that we evolved to be able to eat meat has absolutely no bearing on whether or not we should.