I don't believe so. If the person is capable of attending alone such as being able to answer questions asked to them by staff at the church, Able to do self care activities such as going to the bathroom by themselves, And are aware of not going off with stranger and have no behavior issues then they should be able to attend without an adult or have an adult without disabilities be the one they "have" to speak to.
They are capable, And church is just a public place, Why would it matter at all? I don't get why anyone would think they would need another adult. It is quite dehumanising to say that they need an adult, As if they are not an adult themselves. It's idiocy really.