I would venture to say that the problem with defining evolution as
progress is that it is a useless (and potentially harmful) statement. First,
quite a bit of evolution is retrograde (i.e. loss of functionality),
so saying "evolution = progress" is dead wrong.
So what's wrong with saying "evolution (sometimes) = progress"?
Well, what have you gained by it? Furthermore, you must then constantly
keep on guard against slipping that "sometimes" out of there.
In the end, it's a semantic morass with no scientific benefits.
A case of a related problem:
I once overheard a non-bio major being tutored in basic genetics.
The student could not understand lambda integration into E.coli, because
that would mix "bad" viral DNA with "good" host DNA. It's amazing how
much trouble a few unnecessary words can cause.
Program in Biochemistry, Molecular, Cellular, and Developmental Biology
robison at ribo.harvard.edu