The clear counterargument to that though, in the case of face mounted recording devices, is that they don't force a choice between helping/calling police or filming. True, that should not be a real dilemma, the obvious choice should be to help. The thing is, that problem in crowds of no-one stepping forward to help does not exist purely because of people recording. There are lots of reasons people don't put themselves forward in situations like that. One of them is the assumption that someone else will be able to handle it better than them, or simply waiting for someone to step forward and lead, etc. There are also concerns about liability, possibly about self-endangerment and a dozen or more anxieties and neuroses that can cause the problem. Recording with a cell phone probably exacerbates the issue though, by giving people an activity that, in the moment, their mind can rationalize as doing something. If recording is a less active and more passive process, leaving people free to actually do something and taking away their excuse for rationalization, it might encourage more people to actually help.
Mileage may vary, of course. On balance though, it seems like head mounted recording devices are more of a solution to the problem you were talking about than an exemplar of it.