I certainly can understand the difficulties that ASL people go through. I tout my brother-in-law as an example. He took about 8 years to finish college with a AA degree because of his difficulties in understanding basic English. He has asked me a lot for my help in English.
ASL isn't the problem. I don't know your brother-in-law, so I can't speculate why he personally struggles. But it isn't ASL. Many deaf children have well meaning parents who are told by doctors and teachers that they shouldn't use signs and only communicate in English. Consequently, language acquisition is delayed and the greater degree of deafness, the less access they have to learn it. Early childhood years are crucial for language development. Young children easily pick up a second language from a grandparent, babysitter, or neighbor. Many parents intentionally speak to their children in other languages believing bilingualism to be beneficial. If we believe that, and I do, then it's time we realize that deaf children too will benefit if we promote bilingualism in ASL and English from early ages
But if those years are missed or squandered, language development is more difficult the longer it's delayed. We know from feral children that past a certain point, the ability to acquire any language is gone for good. Whereas, early language development in which one has full access, which means a visual language for deaf children, provides a strong foundation that can be built upon. That's why an adult can learn a second language though a feral child can't learn a first. It does require more effort from an adult than than child to attain fluency.
Some deaf children were only sent to deaf schools or taught to sign only because they 'failed' to learn from oral instruction they couldn't hear. By then, precious time has been wasted and the kid is blamed for the failure of the adults to meet his needs. Those same people who betrayed the deaf children they were supposed to teach cite their English proficiency as evidence of ASL's failures when it's really the failure of oral-only instruction. It will be more difficult to become skilled in either ASL or English. Sometimes in mainstream programs there's so much focus on speech, they're actually taken out of class for speech therapy. Is it really best for the child to be taken out of math class to learn to mimic sounds he can't hear? It happens more than you might think.
ASL can be acquired early and provide that strong foundation for language skill and then be used to teach English a little later. Most of us in America don't understand or appreciate the benefits of knowing more than one language. But if we support bilingualism from early ages, children can attain fluency in both. A large portion of Dutch citizens fluently speak Dutch, German, and American-accented English. Learning promotes more learning. It's time we shed the ill-conceived notion that signed languages are a barrier to understanding the majority language.
I just am thankful that I have an English tutor and a wonderful mom. :)
Oh, I'll never again use the proper tense of "lie/lay/have lain" without remembering my grandmother constantly correcting my grammar. It's certainly important to have someone who's invested in your success.