You can be opposed to something in principle even if you are unable to use it.
I could be opposed to circumcision even though I don't have a penis.
I could think that hair straighteners were the work of the devil even if I were bald.
Someone with a fish allergy could think that sushi is disgusting and say that they wouldn't eat it even if they were not allergic.
You mean that you don't believe that someone dislikes something until you have seen them be offered it and refuse? I think that's silly. I think that people are perfectly capable of having opinions on things that they have never experienced.