I ask because I have been involved in a contentious debate about whether ASL should be a substitute for a traditional foreign language in our core curriculum. My position has been that it should not be because all of our foreign language options are written languages for a good reason. A written language is more powerful than a language only spoken. Written languages have a vast array of cultural resources readily available to the student that are much more difficult to obtain and less extenesive in a language only spoken. ASL depends upon English for its written component, therefore is not an equivalent to other written languages. This doesn't imply that ASL is not a distinct language or a language without a rich culture, only that the study of ASL is not equivalent to the study of traditional written foreign languages.
The fact that cultures with different written languages have different sign languages, may also reinforce the idea that sign language is subordinate to another language if a language is thought to include writing. The contrary view is that videotaping sign language is the equivalent of writing so it is the same as written languages. I think this a partly true, but signers still find writing an important cultural skill and are unlikely to completely substitute writing with videotaping.
I do agree that speaking a language and signing a language are roughly equal.
Is there a deaf ASL or other sign language user here that could comment on this?

420SEL: Why do you think signing is a purer form of expression?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13