Christopher Hitchens used to call this The Argument From Personal Incredulity—i.e. “I can’t imagine an alternative, therefore there mustn’t be an alternative!”, which I always thought had a certain ring to it. But this ‘counterargument’ sort of hinges on the degree to which your interlocutor was actually suffering from a lack of imagination.
I’m glad to see that somebody beat me to it.
Christopher Hitchens used to call this The Argument From Personal Incredulity—i.e. “I can’t imagine an alternative, therefore there mustn’t be an alternative!”, which I always thought had a certain ring to it. But this ‘counterargument’ sort of hinges on the degree to which your interlocutor was actually suffering from a lack of imagination.