You are obviously missing a lot of the plot. Society cannot exist without heroes, just like how society in the real world requires a justice system. There will always be criminals and there will always be villains. Are there problems with the system? Indeed. Change may be needed but the wrong doings of the heroes will never amount to the countless wrong doings of the villains, many for petty reasons. Shigaraki had a sad childhood and he was manipulated by all for one. That does not excuse any of his actions. Shigaraki was let down not by the heroes but by the average people of society. People should stop putting all the blame on heroes and realise that even the average people in society have a duty to protect on another
You missed my reasoning entirely. Being a Hero shouldn't be a profession. What you said about average people other's was correct however in this world of theirs it's illegal to use your quirk in public unless it's for self defense or you have a license. They are content with Heros solving their problems when they themselves should be doing their part.
The whole system the world revolves around is Rotten. Heros shouldn't be a profession and the world is divided into heros and villains Because things shouldn't ever be that simple. While he may be wrong in killing every thing i believe that in order for change to truly happen in this world of theirs is if the system that they follow is destroyed. No more hero assocations no mlre top 10 heros no all might just everday people living their lives with their quirks. Not only that but the Heros are hypocrites at most times. Since they cant be heros without villains or criminals they thrive on conflict and smile saying they saved the day.