A lot of it is. The problem isn't that some people like pineapple on pizza and some don't; the problem is that some people instead go "that pizza has pineapple on it, and therefore it's bad pizza". Which is not how debate works.
If all you're interested in is an exchange of subjective preferences, there IS NO debate. "I like pineapple on pizza" "I don't." "Cool." "Cool." Nothing going on. We can acknowledge that yes indeed we all have our own preferences, and that's the end of it. But that's not what most people are interested in. They want to CONVINCE people of the validity of certain positions - but as soon as you want that, you can no longer bring opinions (i.e. subjective preferences) to the table, because they have no place there. You need arguments.