American Sign Language and other signed languages are languages. It’s important to respect them as languages.
ASL is not English. It is a completely different language. Similarly, signed languages aren’t all the same. British Sign Language is completely different from ASL.
Signs are not universal, any more than spoken words are universal. The meaning of a sign isn’t always obvious just by watching; many signs are completely arbitrary.
Sign is not pantomime, and it’s not ad hoc gesture. It’s also not like symbolic gestures that are sometimes made up to accompany kids songs either. It’s a language, with all the complexities of language. The difference is important, and it needs to be respected.
In order to know what signs mean, you have to learn them. (Just like in order to know what spoken words mean, you have to learn them.)
ASL is not just gestures, any more than spoken languages are just sounds. ASL has grammar, vocabulary, and culture. It’s important to respect this and not erase it.
ASL has vernacular just as spoken languages do; here’s a Washington Post article on how ASL used by African-American communities differs from that of whites.
There exist an incredible amount of sign languages, all over the world. Here’s a list on Wikipedia.
Another thing to bear in mind:
A person fluent in both ASL and English (or Spanish and Venezuelan sign language or whatever) is bilingual, just like a person fluent in Spanish and English or whatever.
This SHOULD be an obvious thing once you grasp that signed languages are real LANGUAGES. But for some reason a lot of people seem to have trouble making the connection on their own and just don’t count signed languages when counting the langages that a person knows.
I once knew a deaf woman who knew 12 languages, including 7 signed languages and 5 written languages. (She does not speak or read lips in any of them, she communicates either by signing or by reading and writing)