Did you ask them their reasons why? Cuz they are against it or were there other reasons?
If deaf of deaf must go to speech therapy then hearing of hearing must take ASL classes. Maybe in their eyes, that is how they see it? Cuz being deaf and using ASL is normal to them just like being hearing and using spoken language is normal to the hearing families. Maybe that's how they see it?
U know what's funny..there is one boy whom I know whose hearing parents are against speech therapy for their son so hearing parents do it too.