I don't think that's a reasonable read; you can't dismiss a specific criticism on the (unsupported) ground that the person making it would totally have dismissed anything at all.
It's a spectacular bit of pride in oneself to try to silence someone's opinion because you found an abstractly-similar statement made by an evil man. Why probe the idea when you could just assign Hitler's evil intentions directly to them?
It's gross. It's tired. I wish people cared more to engage in good faith.
Sometimes, it will be fascism. "It's never fascism" is not a good heuristic.
That's what wartywhoa did to a commenter who was in no way suggesting a fascist view.
That's not worse faith, that's simply pointing out that aligning your ideological opponents with Hitler is intellectually dishonest.
In this you and I agree: "dismissing all criticism because it draws a parallel you don't like isn't reasonable."
If we actually agreed on the principle, you wouldn't be engaging in the behaviour.