I am certainly not intending to intentionally spread FUD, though I guess you probably mean that I am unintentionally propagating FUD spread by other people.

All I mean by saying it's a "logical error" is that it's not an argument which is always valid. Of course particular instances can still be correct.

I think a definition of "proof by contradiction" which includes proof of negation is useful if you are reasoning classically (and this doesn't have to be something you always do, or always avoid; you can reason classically some of the time and intuitionistically some of the time). Although the ideal situation to avoid any confusion would be to have three separate terms, one covering both types of proof and two for the individual types.