Why is utterson terrified of the law and law officers??????

Although Mr. Utterson is considered an honest man (that is a good man) he fears that he will be found for pat misdeeds,

"The thoughts of his mind, besides, were of the gloomiest dye; and when he glanced at the companion of his drive, he was conscious of some touch of that terror of the law and the law's officers, which may at times assail the most honest."

He thinks even honest men can be hunted down for even the most benign of crimes or even blamed for something that they are innocent of.