Bell generally supported teaching lip reading and “articulation” or speech therapy to deaf children (the “Oral Method”) while Edward Gallaudet promoted sign language (the “Manual Method”). Bell and nearly all deaf teachers at the time worried that young people who acquired only sign language based on gestures would not learn to speak and write English adequately, and could not communicate with other members of society. But the differences between these two approaches were not as clear as believed today. In reality, both Bell and Gallaudet supported versions of a “Combined” method.
In promoting with the Oral method, Bell was not trying to “eradicate deaf culture” but to help deaf children live fuller lives, integrated with their families and communities.
It is false to say Bell was totally opposed to signing. He taught signing to many of his students, and was an instructor for two months at Thomas Gallaudet’s American School for the Deaf in Hartford, where rudimentary ASL was developed. He gave a speech to the student body in sign language.
“I admire the language of signs as heartily as any teacher can desire,” Bell said in a speech to teachers at the National Educational Association convention in Wisconsin in 1884. “It is a beautiful language.”
When linguists disparaged signing by saying it wasn’t a legitimate language, Bell came to its defense in a letter to The Educator in 1898. 
Bell routinely signed with his wife, Mabel, who was deaf. His last words on August 2, 1922 were signed to her. “Even after the pulse could not be felt, his fingers kept moving in the last feeble effort to comfort & encourage his wife,” Mabel wrote to a friend a few days later.
- National Education Association, Proceedings of meeting held in the Senate chamber, Madison, Wis., Wednesday, July 16th, 1884. https://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t49p30g1g&view=1up&seq=7
- The Question of Sign-Language, The Educator Vol. V, pp. 38. 1898 https://www.loc.gov/item/magbell.37600801/.
- Mabel Hubbard Bell to Mr. MacKinnon. August 16, 1922. https://www.loc.gov/item/magbell.25210207/.