are quick to label such criticisms as "fanboy" talk.
It's just a Circumstantial Ad Hominem logical fallacy: Attack a claim by asserting that the person making the claim has some self-interest in making that claim. A Circumstantial ad Hominem is a fallacy because a person's interests have no bearing on the truth or falsity of the claim. While a person's interests will provide them with motives to make certain claims, the claims stand or fall on their own.
Example:
Person A says "The glaciers in Glacier National Park are melting."
Person B says "You would say that because you are a tree-hugging liberal."
It's the kind of intellectual shallowness and laziness that all-too-often passes for debate on the Internet.