Bhagavad Gita, Chapter 17, Verse 19

That austerity which is practised out of a foolish notion, with self-torture or for the purpose of injuring another, is declared to be Tâmasika.

Real harm, to oneself or to others, is named here plainly as the mark of this lowest mode.

Krishna doesn't soften this description, confusion leading to real injury is stated directly. Nothing about this mode is left ambiguous or excused.