Which won't happen as criminals will never want themselves filmed and they are the ones you want to film to make society better and protect yourself.

Haven't you got that the wrong way around?

If we have to come up with a technological solution to grant anonymity when people are filming, criminals can use it.

If we as a society don't go around filming everyone all the time, we don't need that technical solution available, so we can film the criminals when they are doing something criminal.