Working with the Double Negative – Is my microphone on, or not?

I’m in a Skype for Business call and I’m getting confused by the blue button in this screen:

In maths and in the English language it’s quite clear that a double-negative is a positive:

“I can’t not smile when she does that”

Means:

“I smile when she does that”

Or in maths:

0-(-1) = 1

likewise

0+(-1)= -1

The icon on this screen is the mute icon – so that’s (-1) and the icon is highlighted so that’s + resulting in -1 which means that the sound isn’t flowing therefore I’m on mute?

That’s makes sense, and that it exactly what happens.

mute icon highlighted = on mute

But, I can’t help thinking that this is all more complicated that it needs to be. It would be far less confusing to use a microphone icon rather than a mute icon. Then icon selected would mean microphone on and icon not selected would mean microphone off. I wouldn’t have to run an logic equation in my head to be confident that I wasn’t that annoying person on the call who’s disrupting everyone else by the high levels of background noise.

For me it’s just not intuitive for it to be a mute button.

I suppose it’s back to Norman and his doors.