According to one interpretation the "yarei v'rach ha'leivav" mentioned in Parshas Shoftim who may return from the front lines of battle refers to someone who is "yarei m'aveiros b'yado," someone who is afraid of the many aveiros he might have done.
Even someone who violated a "minor" aveira like speaking between putting on his tefilin shel yad and shel rosh was excused from battle. The soldiers the Torah envisions are tzadikim (ironic that today it's a mark of tzidkus to avoid fighting for our country). Why then is the "yarei m'aveiros" excused -- surely this attitude represents an ideal of yiras shamayim we should seek to emulate?
To answer this question we need to do a little chazarah of a vort of the Sefas Emes from 2 years ago (link). When Sarah heard the visitor to her home say that she would have a child, Sarah laughed. Yet, when challenged by Hashem, Sarah replied that she in fact did not laugh. How could Sarah deny reality when speaking directly to Hashem?
The Sefas Emes answers that Sarah realized that her laughing was wrong and she immediately did teshuvah. Such is the power of teshuvah that the past is totally wiped clean -- a person can start with a totally new slate. Sarah could legitimately say that she did not laugh -- the past was as if it never happened.
The fact that a person continues to be "yarei m'aveiros b'yado" shows that either a person has not done teshuvah properly or does not fully believe in or appreciate the power of teshuvah. Yiras shamayim - yes. Yirah from aveiros -- wrong attitude.
Elul should be the happiest month of the year. It certainly is a solemn month, a month where we have a serious responsibility to do teshuvah. Yet, fulfillment of that responsibility can lead to complete renewal, all past deeds forgiven and forgotten, and what could be better than that? R' Chaim Volozhiner records in Keser Rosh (#104) that the GR"A was filled with simcha during tekiyas shofar. All those stories and sichos of the ba'alei mussar about the importance of Elul are there to get us to focus on what we have to do and to take it seriously -- not to depress us.
One of the more well known stories In Halakhic Man (p. 60-61) is the episode of the ba'al toke'a (a Chabad chossid) who began to cry just as he was prepared to blow shofar. R' Moshe Soloveitchik turned to the ba'al toke'a and asked him whether he cried when he took his lulav as well. If both are mitzvos of Hashem, shouldn't we respond the same to both? The Rav goes on to explain that the chossid was responding to the mystical meaning behind the mitzvah of shofar, which, according to the Alter Rebbe, represents a wail of longing to reunite with the Shechina, to transcend the unbridgable gap between material reality and higher spiritual realms. His father's attitude, the attitude of halachic man, is that there is no need to cry over that gap, as G-d's presence can be found in the objective reality of this world as reflected in halacha; there is no need to seek an escape to higher realms. R' Aharon Soloveitchik interpreted the same story a bit differently (link). The reason his father frowned on the tears of the ba'al toke'a was because "chedvas Hashem hi ma'uzchem" -- Rosh haShana is not a day meant for tears; it's a day meant for joy. Given the mesorah R' Chaim Volozhiner quotes regarding the GR"A, R' Ahron's interpretation of his father's response makes perfect sense.