The reason is: all continuously living human beings, will prefer to eat other living things, and not want to be eaten by other living things.
Alternative wordings of your question might include, "Is it practical to live without hypocrisy?", or, "Is it possible to apply the golden rule to all acts consistently?"
If I understand you as you mean, then you would define "holding a double standard" as
desiring to act upon a self-like class of entities while desiring not to be samely acted upon by that class of entities.
public void Eat(LivingThing& anotherLivingThing);
Instantiations of this class would be holding a double standard if they desired to invoke
LivingThing::Eat while desiring not to become the parameter themselves.
I use this example not (only) because you have 17,874 reputation on Stack Overflow :p, but because, for me at least, it isolates the major ambiguity: What constitutes a
Would you consider microorganisms in the air
LivingThings? Or only multicellular organisms? Or perhaps, only multicellular organisms with sentience, i.e. not plants?
To be "eligible for double-standardness," do two entities need to be
LivingThings, as in, be instantiations of the base or a derived class, i.e. must they be linked by a nature of what they are? Or, do two entities simply need to do things that
LivingThings do, as in, implement a common interface (er, abstract class), e.g. is it a double standard for us to desire to destroy a computer, if we also desire not to be destroyed by a computer? (In this context, personally, I believe the object-oriented and functional views are the same.)
I understand that "living things" was only one example. But generally speaking, and maybe this is what Rex Kerr was getting at too, I believe that no matter what you talk about, the same ambiguities would arise, because lumping and distinction are operations local and subjective to our brains.