Idiom oddity

Noticed an odd pair of phrases.
In question and out of the question mean more or less the same thing.

Walking today is in question.
Walking today is out of the question.

The second is more certain, but both mean that I shouldn’t walk.

Logically the converses,
Walking today is out of question.
Walking today is in the question.

should mean that walking is favorable. But they aren’t valid phrases at all.

= = = = =

Another mispair: Affronts and arrears should be opposites. Instead, affronts are insults and arrears are back rent. The first seems disconnected, the latter is logical enough. Looking it up, affront means a slap to the face, from Latin ad frontem.