Yes. you are, if you are concerned about the children and not the school. If you are concerned to know that the behaviour of all pupils, whether sn or not, will be managed appropriately so that it impacts as little as possible on the education of your child then no, that is not unreasonable.
The question is - will children be supported appropriately? If not, then it's not a good school.
Your child will benefit from being around people of all abilities and learning that there are a lot of different people in the world, and how to interact with people - all people.
I have 2 children with autism and I am trying to not be offended and to see your pov. FWIW, my boys are lovely people, very kind and caring and imo any child who knows them is better for it! [proud mum]. Yes they need support, but mainly to access the curriculum, not to manage their behaviour. And yes, they need help to focus, but they don't cause problems for other children, because they get that support.
Some of the most disruptive children I have known are those with no sn or sen. tbh, they are the ones you should be concerned about.
Find out about the school, find out how they operate.
and finally, please try to see that there are many kinds of sn and sn does not equal trouble.