If you get into an argument with a teenager, he can technically then claim that the point is "arguable." After all, you are arguing it, right? Case closed.
If the point is arguable, then both sides have some legitimacy, and in particular, it means his side of the discussion must have some legitimacy, even if it has precisely zero logical supports. This means that one view is pretty much as good as another, so his view is just as good as yours. Therefore, he chooses his, and thinks you have no logical grounds to contradict him, because it's "just your opinion."
Let me note in passing that my five sons seldom or never argued in this fashion. Not to my face, anyway. They might have done so as they walked away muttering. Son #4 when purchasing a truck he could in no way afford, did once say "You always talk about what could go wrong!" Which is true.
I thought of this when I read an account today of how the 1619 Project has "sparked discussion." It has not sparked discussion. It has sparked condemnation from people who actually know something about the topic, which is not the same thing. It would be as if Sports Illustrated put its official weight behind the Hall of Fame candidacy of Moonlight Graham, on the slender basis that he figured prominently in a really good baseball movie and upon review, did actually play in the major leagues a century ago. (BTW, he played for Manchester, NH in the New England League as well.) When every sane baseball fan in America (and the Caribbean) wrote lengthy essays in protest, SI might attempt the dodge that they had "sparked debate" and that this somehow added to Graham's legitimacy as a candidate, but that would be simply ridiculous.
This happens in the arts, that people try and "start a discussion" about what we consider to be art, or what society is all about, or whether sharks have tails, giving the individual a forum to blather endlessly - which was the original goal. It doesn't make it right.