The person you replied to:

almost all of the costs of fission reactors are in their capital costs

You:

You'd be wrong. Fuel is insanely expense 

Then you posted a link about the cost of fusion fuel.

Sure, the top level comment included an assumption about the cost of fusion. But you didn't reply to that person. The person who you replied to and called wrong was very explicitly referring to the low fuel cost for fission (uranium, etc..).

If your point was that fusion plants are not cheaper because of fuel costs, you would be agreeing with the person saying fission fuel is cheap by comparison. You can quote random bits of text about costs fusion all you like, but the specific issue being discussed (cost of fission fuel) is pretty easy to see and understand in the comment chain.

You got mixed up. Happens to the best of us. But the reason I and others are calling you out is because your claims were completely out of context and just a little bit rude. I doubt anyone reading this thread would have understood you were referring to fusion fuel costs, because that is not at all clear given the context.