To answer the title of your post, physics can be manipulated, similar to other sciences, philosophy and religion. A sensational example is offered by one Dr. David Grimes, a physicist who claims he has created a formula that can magically tell us if a particular conspiracy theory is valid.
The article I linked to below appears in PLOS ONE. And if you don't think it's an authentic scientific journal, note that it's "peer reviewed."
On the Viability of Conspiratorial Beliefs -- David Grimes, PLOS ONE, January 26, 2016
However, the example you cited - the multiverse - is a little different. I'm not clear how it might be used for propaganda purposes. It sounds like a perfectly credible, if offbeat, theory.
It might qualify as "useless" in the sense that it's hard to imagine how we could realize any practical benefits from such a theory in the near future. If we could discover another universe with another planet exactly like Earth - but unpopulated and unpolluted - then somehow transport seven billion people from Earth to its distant cousin, then all this multiverse research might have practical significance. Of course, that's never going to happen.
In the meantime, I don't understand the problem with scientists speculating, theorizing and expounding on black holes, wormholes and multiverses. Isn't that what science is all about - asking questions and pushing the envelope of the known?
As others asked in the comments, why does a particular scientific inquiry have to be "useful"?