A common line of argument against Donald Trump's repressive proposals for Muslims is that Trump is the best thing that could happen to the self-styled Islamic State, or that the IS or Daesh couldn't ask for a better American ally than Trump. This is really the same argument you hear whenever repressive measures are proposed against a violent or merely radical organization, and in this case it strikes me as lazy thinking. It forces the current terrorist movement into an old, arguably irrelevant mold.
In the late 19th century, violent anarchists developed the idea of "propaganda of the deed" that appeared to justify terrorist action, whether it was effective or not. A terrorist deed's propaganda effect was supposed to be twofold. If successful in its original objective, by blowing up a building or killing a politician, it exposed some weakness of the oppressive state. The second effect is known as the provocation-repression theory. According to this theory, a terrorist attack was successful if it provoked new repressive measures by the government. Anarchists hoped that these new repressive measures, by in some way curtailing the liberties of people in general, would expose the essentially repressive, tyrannical nature of the state to more people in a radicalizing way. This strategy never worked; in most countries it fell to a minority of civil-libertarians to defend anarchists as a whole, including the non-violent ones, from majoritarian demands for violent repression by the government or, as many Americans wanted after the assassination of President McKinley in 1901, a ban on admitting immigrants who espoused anarchist views.
I'm no student of anarchist movements, but I doubt that repressive measures anywhere actually inspired growth in anarchist ranks. Despite this failure, some academics, and more laymen, seem to think that the provocation-repression process actually can work the way the anarchists hoped. This assumption explains the puerile argument that Trump is doing the IS's work in America. The argument itself assumes that the measures proposed by Trump, if not Trump's mere proposal of them, are sufficient to radicalize more Muslims here and abroad. For some it may go further, their idea being that the IS or supporters like the San Bernardino shooters carry out their attacks in order to provoke the repressive response that will truly radicalize Muslims. Here, for once, the old reactionary argument that certain people wrongly "blame America first" for everything bad in the world has merit. By now, with the rise of the IS, we're past the stage at which the terror war could be described as a "defensive jihad" to which the correct response would be some change in American behavior, be it more equitable treatment of Muslim countries or total disengagement from the Middle East. With the proclamation of a caliphate it's more correct to speak now of an Islamist offensive with a momentum and motivating logic of its own. I doubt greatly whether the IS requires or even wants Trump to do his thing, although they'll probably try to milk it for something. My hunch right now is that the IS in particular is driven not by a continued narrative of infidel oppression but by a perceived winning streak. If they can keep pulling off attacks, or inspiring them, and if they can hold out in Syria and Iraq under the chaotic assault of neighbors and superpowers, that's what will inspire people to swear allegiance, not some beef with Donald Trump. If anything, the IS might use Trump as proof of how scared Americans are of them right now, with the emphasis not on any threat Trump may represent to Muslims but on how powerful the Daesh must be to inspire such fear. That's no more an argument against Trump's stand than the provocation-repression theory. There are real arguments to be made against Trump, but his seeming hysteria and simplistic thinking shouldn't provoke hysteria and simplistic thinking among his critics. Trump's antics are unlikely to help the IS in any measurable way, but it's even less likely that stopping Trump will stop the jihad, or even slow it down.