You're doubling-down on your mistake, by pretending the first clause of the sentence--which bounds the category--didn't exist.

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Me: "Futuristic [thermonuclear power] doesn't necessarily mean [fission], although I doubt something else would be widespread in in just one decade."

You: "OMG, what about wind and solar!? Lots of things have already been replacing fission! So out of touch."

Me: "I said types of thermonuclear power that aren't fission. Not power in general."

You: "Yes you did if I just... delete the entire first half of your sentence..."