As I see it the flashlight analogy is employed to demonstrate the differences between accessing a 1-way service versus a 2-way service.

If I willingly receive stray light from my neighbor, and take advantage of it without affecting his own use, there is no harm.

If I tap into his wifi without permission (note that a wilful act is required in initiating and/or accepting the connection, whereas receipt of stray light is passive), which automatically and unavoidably affects his own use, there is harm.

Conversely, if his lights intrude into my house I can file a civil complaint because visible spectrum isn't affected by the FCC interference code the way radio spectrum is.