It is an argument ad absurdum, which isn't an invalid argument though it can be emotionally charged It is not argument ad absurdum. It's true that sometimes,

It is an argument ad absurdum, which isn't an invalid argument though it can be emotionally charged It is not argument ad absurdum. It's true that sometimes, it helps to use an exaggerated example to illustrate a nuanced point. But in this case it isn't that people don't understand there are lines. The point is superfluous, and you get to bring up Nazis yet again in comparison to border control. It's rhetorical tactic, not an argument. For reference, argument ad absurdum is actually the opposite. That's when you take a logical premise to its extreme to show how it's a foolish proposition. In this case, the extreme example was in support of the proposition.