I think people who fear hell often reform their ways, I know that for along time I was just using God I wanted to go to heaven and I wanted to avoid hell .... this was the only reason  I obeyed God's commandments.

That said I do not think avoiding sin out of fear of hell absolves us from guilt rather we sin in our hearts for God knows internally we still desire to sin.

I originally misread your question, I am sorry. I think the reason that fear of hell does not always cause people to avoid committing a sin is the simple fact that when the preform the sin they desire to commit the sin more than they desire to avoid hell .... everything we do we do because we desire it.

This is a great thread, Spouse.  I think fear of hell can help us not sin.  But fear is not the strongest feeling for it can be cast out by love.  Fear of hurting Jesus because we love Him, is the strongest feeling.  Love is the strongest feeling.

You will notice that most on this forum have no use for feeling, emotionalism.  I believe emotion to be our driving force.  I believe we must inform our emotions with right reason and then use them to get us where we need to go.  But fear can only be tolerated for so long, while love can take us from task to task and build us up at the same time.  

Sometimes as we go through the day, we don't think in terms of heaven or hell, but only of whatever is at hand.  It takes a deep love which thinks of the "other" to view all things in the light of whether this thing is good or bad.

What keeps me thinking about the existence of Hell is
that the Church teaches that it is real.
I keep thinking of Fatima when the Blessed Mother
opened up the earth, and showed Hell to the
three children.
Because of the pagan environment that we have to live
in, it is so easy to forget the consequences of sin, and
there eternal consequences.
What has happen we replaced God, his commandments,
and his church with the worship of man, and the state.
Most people are influenced in the way they think, and
their life style. The Mass Media, modern communications,
the wealthy elite whom controls the flow of money, and
credit in the world are responsible in moving people
in the direction of avoiding the truths that is leading
them to hell.

I hope you don't mind but I'd like to share something personal along this topic.  Last week we were coming back from our son's college orientation.  Around 9pm we made a bathroom stop for our 4 year old at a gas station/convenience store/ice cream shop.  Outside sitting on a bench enjoying an ice cream on a really hot summer evening were a grandma and her two small (about 5 or 6) grandchildren.  At the gas pump was a car with a young woman about 20 or so arguing with her current boyfriend and an old boyfriend.  It was really loud and quite vulgar.  I covered my sons ears as we went inside.  As my husband was coming out, the grandmother went to the young girl and very politely asked the group to please stop using the vulgar language or to take the conversation elsewhere--her grandchildren were watching.  The young girl and the boys got right up in the lady's face and for a moment I actually thought they might hit her or something.  They all shouted something vulgar and told her to mind her own business.  As we were leaving my husband made a the comment, "I'm glad that there is a hell."  I asked him why and  he responded, "Because otherwise I'd take my gun and shoot those three hoodlums in the head."  I'm not sure what that actually says about my husband but on some level it makes sense---Most of society, and some Catholics included, no longer have a fear of hell at all.

Well he had a slight temptation there.  But notice how he chose the good.