It is indeed cut and dried. Especially with reference to the question of evolution. If evolution is about descent then a proper definition, an objective one, of species is essential. The only criteria which is totally objective is reproductive viability. It takes into consideration all the biological factors of descent. Any other definition is subjective and prone to manipulation.
Nonsense. Where is this writ? Is an absolute and comprehensive definition of a star a requirement to do stellar astronomy? In your dreams.
The only criteria which is totally objective is reproductive viability.
What? Since when is "total objectivity" a measure of the reality of a natural phenomena? Unfortunately for your argument, a mare doesn't pay too much attention to questions of "total objectivity" or "reproductive viability" when a comely donkey is in heat and in the local vicinity.
It takes into consideration all the biological factors of descent. Any other definition is subjective and prone to manipulation.
What is this, Absolutist night? Even if you hold your breath until you turn blue, there is no detectable barrier between species that corresponds to zoological species charts. There is only relative speciation, along a varied spectrum, of one creature with respect to another. If you think speciation is a tangible barrier with tangible physical existence, kindly put it up on the microscope stand so we can all look at it.
It is just a classification idea which creationists treat as if it were a law of nature--it ain't. All definitions are, in some measure, subjective and prone to manipulation. As has been pointed out to creationists on innumerable occasions, the social impact of an idea, including how subjectively manipulable it is, is not a valid measure of it's truth.