What characterizes the men who fight on Macbeth's side? How do they feel about what they do?

The men who fight on Macbeth's side do so because they are afraid of him. He has learned that no one respects him and that consequently he must rule by fear. They know that if they were to flee Scotland or join the approaching English army, Macbeth is fully capable of taking his revenge on their families, as he did with the family of Macduff. Macbeth is fully aware that there is no loyalty among his followers. In Act V, Scene 3, he acknowledges this fact to himself.

I have lived long enough. My way of life
Is fall'n into the sear, the yellow leaf,
And that which should accompany old age,
As honor, love, obedience, troops of friends,
I must not look to have; but, in their stead,
Curses, not loud but deep, mouth-honor, breath,
Which the poor heart would fain deny and dare not.

Naturally the men are not going to be very courageous fighters. Macbeth knows that the forthcoming battle is already lost. The fact that he is a king with such an army is one of the things that troubles him the most. Men are deserting him throughout the last act. Even Seyton, his chief assistant, treats him with cold, formal courtesy which hides his contempt. Seyton appears frequently at the end in order to represent the attitude of all of Macbeth's officers, and by inference the attitude of the lower ranks. Macbeth expresses himself with anger through Act V. This is because he is depressed, frustrated and infuriated by the endless desertions. When Act V, Scene 3 opens, he is issuing a general order which shows his desperate position:

Bring me no more reports; let them fly all!

Many officers have been coming to him with reports of desertions. If this keeps up he will be defending an empty castle. He will have nothing left to rely on but the predictions of the witches' apparitions that no one can harm him until the woods of Birnam come marching toward Dunsinane and unless he engages in hand-to-hand combat with a man who was not of woman born. Ironically, Macbeth tries to rule by fear to stop desertions, but his fear tactics don't work; they are only driving more and more men away. If everybody deserts him, he will have no soldiers left to enforce his fear tactics.