Good Isn't Scary

In many philosophies, one of the most important qualities of a good person is mercy, even to enemies. One of the ways to contrast the heroes and villains is through the fear that villains inspire in others. The characters know that the villains are not above torture or retaliating against innocent loved ones, and for that reason they are much more cautious about crossing the villains than the heroes.

This often results from the assumption on the part of the characters that Good Is Impotent, when it might be the case that Good Is Not Nice or Good Is Not Soft after all. It may also be linked with Thou Shalt Not Kill as a result of other characters being aware of how it's impossible for them to follow through with their threats.

On some occasions, this trope can work to the advantage of the heroes. If they have a reputation for being merciful, enemies might be more willing to surrender to them. (This might be a separate trope.)

Contrast Dark Is Not Evil when a good character does have a very intimidating manner or appearance and could scare people without even trying (or intending to at all). For instance a vampire in a medieval setting who scares the crap out of everyone, yet he's one of the heroes. This person could intimidate even bad guys with ease and get information out of them merely by showing himself.

Fan Works
"One reason the Warriors are as successful as we are is that in any given opportunity, we will field far more force that is far nastier than the enemy is prepared to deal with. We don't fight just to win. We fight to crush the enemy utterly. We fight to overwhelm and destroy."
 * Deliberately averted by Douglas Sangnoir and the Warriors in Drunkard's Walk:

Literature

 * In Harry Potter and the Goblet of Fire, a band of Death Eaters runs amok at the Quidditch World Cup, while the Ministry tries in vain to control them. Once an unknown party conjures the sign of their former master Voldemort, they immediately flee, fearing the punishment they'd get for denouncing him after he fell.

Live-Action TV

 * In the Star Trek: Deep Space Nine episode "The Maquis Part II", Captain Sisko and Gul Dukat go to investigate rumors that the Cardassian state has been smuggling weapons to their colonies in the demilitarized zone, using a free traders as an intermediary. When they encounter such a ship, Sisko's polite request to allow them to search it is met with refusal.  Dukat then forcefully demands that the captain comply on threat of death, with much greater success.

Video Games

 * In Fallout: New Vegas, the player character can get hired by the NCR to interrogate a captured officer of  Caesar's Legion.  The prisoner, a Centurion named Silus, has been extremely uncooperative due to his knowledge that he's protected by the NCR's laws against torture.  The best solution to this quest is to convince him you were sent by the Legion to punish him for allowing himself to be captured. Doing so immediately inspires panic and indignation in him, and in speaking in his own defence he accidentally reveals information on several topics of interest to the NCR.
 * This is because while an NCR goon (the designated good guys of the story) does not instill fear in Silus at all, an agent of Caesar's Legion does. Even though the main character might be bluffing, Silus doesn't take that chance; he seems to realize how ruthless a servant of The Legion can be.

Western Animation

 * On the Justice League cartoon, the heroes sometimes have trouble getting answers from captured villains and minions for this reason. Superman and the Flash especially get no respect, though Batman usually does, and occasionally, others take a leaf from his book and make it work.