Arguments about the meaning of words pop up all over the place. Let's rely on standard dictionaries to resolve these disputes, starting with flammable/inflammable.
The online Oxford Dictionary says:
The words inflammable and flammable both have the same meaning, ‘easily set on fire’. This might seem surprising, given that the prefix in- normally has a negative meaning (as in indirect or insufficient), and so it might be expected that inflammable would mean the opposite of flammable.Dictionary.com also considers the words to be synonymous. It notes that while inflammable is older than flammable by about two centuries, flammable now is used more technically, again to avoid confusion with the negative prefix, while inflammable is used in nontechnical or figurative contexts.
Bottom line: Go with the word that minimizes confusion: flammable.
