My Hero Academia takes place in a world where supernatural Quirks are the norm, for better or for worse. Most people's Quirks don't have much impact on daily life, such as David Shield's bendy fingers or Inko Midoriya's ability to attract small items to her hands. Other Quirks, however, such as Bakugo's Explosion or the famed One For All, are in a totally different league... and can be a double-edged sword.
Weak or obscure Quirks aren't enough to take down villains on the street, but an excessively destructive or messy Quirk might cause as much harm as the villains would. At some point, is the destruction caused by certain powerful Quirks not worth the benefits of fighting the bad guys with them?
The Most Destructive Pro Heroes & Their Carnage
With the right training, any sufficiently powerful Quirk can help a hero take down villains. From the start, though, it was made clear that some Quirks require far more discretion and restraint than others. For example, Mt. Lady, introduced in the series' first episode, is a fine hero, but her colossal true form is destruction incarnate. She can trample cars and trucks underfoot, use trains or small buildings as clubs to bludgeon villains and would cause untold devastation if she's knocked down. The actual My Hero Academia lore confirms that Mr. Lady has a problem with collateral damage, and she's not alone.
Endeavor, the #2 pro hero, envelops the entire battlefield in flames, and he has a temper to match. When Endeavor fights, he doesn't mind blasting holes in nearby buildings or shattering the street underfoot, if it means taking down his enemies. Endeavor delivered a terrific blow to the Hooded Nomu at the end of Season 4, but while that was a great victory, Endeavor cause as much collateral damage as his monstrous foe, if not more. His son, Shoto Todoroki, is on course to fight the same way and wreak havoc in the line of duty. Unlike Endeavor, Shoto can also generate many tons of heavy ice, which can crush vehicles and crack the streets under the sheer weight.
Even All Might causes devastation everywhere he goes, though he's also known for rescuing injured civilians as well as throwing punches. When All Might wields the true power of One For All, he can deliver terrific Smash attacks that generate hurricane-like force, and a single California Smash threw a villain to the ground and created a massive impact crater. Should heroes keep fighting like this and cause headaches for the rescue and repair crews who arrive after the battle?
When & Where To Use Destructive Quirks
It may be too much to ask for destructive heroes such as Mt. Lady, Endeavor and All Might to simply change their fighting style or give up their careers. Such powerhouse heroes are vital for battling the most terrifying villains. When Izuku Midoriya fought the villain Muscular, only sheer brute force could win that fight. Similarly, Endeavor couldn't just talk his way out of fighting that Hooded Nomu. All the same, however, this constant carnage is bound to add up in terms of infrastructure costs. Every time All Might destroys a villain with a Smash attack, he's making a huge crater in the road, and that's going to block traffic in some rather busy cities. No business will be happy to have a huge hole blasted into its skyscraper because Mt. Lady threw a kick. What can be done?
For the most part, this is why heroes with more precise, subtle Quirks are used more in densely populated urban areas. Think along the lines of Eraser Head, who uses his Quirk-disabling eyes to render a villain helpless and capture them without any carnage or bloodshed. The more destructive heroes may put their powers and talents to use by meeting the most destructive villains head-on, in situations where a lot of property is about to be damaged anyway. Ideally, destructive heroes like All Might and Mt. Lady will show some restraint in urban areas and save their firepower for only the most destructive villains.
This might limit their opportunities to fight, but if it gives the repair and construction crews a break, it may be worthwhile. Such heroes could also hunt down villains in rural areas or intercept them on country roads, where far less property stands to be damaged or blown away. If at all possible, the pro heroes might even lure villains out of a city and to the outskirts, where a fight can take place without serious risk to property or innocent bystanders. Out there, All Might and Endeavor can cut loose, while the likes of Eraser Head and Best Jeanist can capture and restrain urban villains without rendering entire city blocks unusable.