Even though i support FOSS over OSS, I've always found this particular argument a bit uselessly pedantic. Both of these term are almost always used casually not legally, when we want to do that (i.e when releasing software) we must use the highly specific language of a particular license anyway... which leaves only the following argument:
> establishing freedom in a lasting way depends above all on teaching people to value freedom.
For non-enterprise uses, how much OSS is not also FOSS? most people assume they are equal because the free part is implied, so do we really need to teach it? most software vendors understand this because they know the majority of people will just use it for free if the source is available regardless of whether it is explicitly given as free. It's too hard to enforce payment in any area except for enterprise... When this market force already exists, does it really help to create a social force to differentiate FOSS from OSS? I'm not sure, I think you just end up pissing off new FOSS enthusiasts.