the reason probably wasn’t so that Harry could say, “dementors are bad” again.
It could be there to highlight the moral bankruptcy of the Wizengamot and also mislead the readers into searching for a stereotypically heroic solution (vanquish the monster and rescue the fair-complexioned maiden!) when cleverness is called for.
Slowly, Harry Potter sat back down again as Professor McGonagall pulled down with her grip on his wrist.
But by then he’d already declared war on the country of magical Britain, and the idea of other people calling him a Dark Lord no longer seemed important one way or another.
It could be there to highlight the moral bankruptcy of the Wizengamot and also mislead the readers into searching for a stereotypically heroic solution (vanquish the monster and rescue the fair-complexioned maiden!) when cleverness is called for.
Indeed: