Complex sentence: Supporters of ASL or the manualists claim that SEE and its cohort system, Cued Speech, robs children of belonging to a culture that they can fully participate in, is hard for deaf children to master and does not result in those children being competent with English.
Split into simpler sentences: Supporters of ASL or the claim that teaching deaf children SEE deprives them of belonging to a culture that they can fully participate in. They also claim that SEE is harder for deaf children to master and does not result in those children being competent with English.