Never judge a philosophy by its abuse

[Pyrrho]

I honestly still don't know what the phrase means.

In practice, it often means that someone else is interpreting something differently from the speaker, and the speaker objects to that and calls it "abuse."

However, EvidenceVersusFaith gives an interesting case about Epicurus.  I am not sure that I would call that an "abuse" of a philosophy so much as a total misrepresentation of it.  It is ironic that being an epicurean (in the modern sense of the word in English) means almost the opposite of being an Epicurean (follower of Epicurus).  That is because the Christians (and some others) did not like his idea that pleasure was the good and pain was bad, and so they gave a version of that that otherwise bears no resemblance with what he advocated.