What suggests that the speaker's attitude toward the wall is not necessarily Frost's in "Mending Wall?"

Reading this poem over several times, I looked for
something that seems to contradict the general mood of the
poem.

The poem is about mending a wall between two
properties, something the speaker and his neighbor do each spring. The speaker compares
the activity to a game. Philosophically, he also suggests that it seems to be ludicrous
to even have a wall because neither man owns animals that might
wander without one, and the two different species of trees they grow will not cross the
wall or interfere with each other in any way.

Up until this
point, the poem has been entertaining. The shift I notice is at the end of the poem. It
seems that the wall is there because it has always been there, because the neighbor's
father wanted it there. There seems to be no other reason. Frost's writing seems to cast
doubt on the wisdom of such an attitude with the following
lines:

He
only says, 'Good fences make good neighbors'...

He moves in
darkness as it seems to me~ 
Not of woods only and the shade of
trees. 
He will not go behind his father's saying, 
And he likes
having thought of it so well 
He says again, "Good fences make good
neighbors."

The tone with the
line "moves in darkness" changes the mood of the poem for me. The sense I get from this
line is that the neighbor acts not of his own free will, but because he had heard his
father say this many times. In that these men seem to have been rebuilding this wall for
many years, perhaps Frost is puzzled that the man cannot, after all this time, decide
whether he feels the wall is necessary at all.

On the other
hand, perhaps the title, "Mending Wall," is a play on words for "mending fences."
Perhaps in the past there was a need for a wall separating the properties and the author
simply wonders why the neighbor cannot decide about the wall on his
own.

The end of the poem, however, suggests, with the
introduction of an image of the man walking in darkness, that Frost may not have the
same sense that fixing the wall is like a game, or a time of camaraderie as the speaker
seems to infer. It simply may mean that Frost cannot make sense of how the neighbor's
mind works.