Well if some or all of what you say is partly or wholly true you are talking about unintended consequences that had been unpredictable, which applies to all conflicts when you think about it, and I think "naive" is a bit strong. Whatever bad things were unintentionally exacerbated by the International Brigades, they have left us an enduring legacy, as with the Cable Street anti-Mosley protest, of ordinary working people showing that they are not prepared to tolerate fascism. A pretty big positive, I'd say.