SUPERHERO /ˈsuː.pəˌhɪə.rəʊ/ /ˈsuː.pɚ-/ noun [ C ]
1.                    a character in a film or story who has special strength and uses it to do good things and help other people.
2.                   someone who has done something very brave to help someone else.

Coming from the words super and hero, they were merged into a noun word defining someone who has a special strength and uses it to do good things, well basically getting rid of the villains into phantom zone, or helping people whose houses are in fire, stopping robbery maybe. But yes, they are human.

Human means...

They are the fully developed mammalians? They are the bestest creature that could exist in the world with plus super power. They fall in love, right? Do they have rage? Lust, at least? 

Among hundreds, thousands maybe of superheroes, they all have their own altruism, history of why they have the 'super' word attach to them, or simply a motive of why the dedicate their lives for society's good.

Like, Spiderman!

Peter Parker happened to get bitten by an irradiated spider that turned him into physiologically mutated human and granted his powers superhuman strength; reflexes; and balance, and his special spider web shots that keep him clinging indomitably to most surfaces.

Or, Batman?

The playboy and wealthy Bruce Wayne who live in resentment at his parents murder relies on his genius intellect, physical power, detective knack, and science and technology to eradicate criminals in Gotham.

Maybe, Captain America.

Through super-soldier serum and vita-ray treatment, he was transformed his strength, agility, and rapid recuperating are at the zenith of natural human potential.  

Do we need them?

The images of superheroes tend to be inherent with the depiction of super criminals city, conceiving the idea of how powerless the law is, portraying of how incapable the police officers are. It's a grim circumstance in which I never wanted to go, no one wants to. This is the first justification why I don’t want superheroes exist in my real life. I have ninety-nine problems, but those monsters and zombies won’t be ones.

Secondly, in the idea of justice. For whom?

Our law has regulated as just as it could be on everyone involved, for the criminals, victims, also witnesses. Justice should be created for every human being regardless their bad deeds.

In many scenes of superheroes movies, the act of their defensive action turned into violation of human rights. Rights to be presumed as innocent, rights to attend the court for trial, and many things that have been ruled in law, such as

Miranda Rights:

The circumstances triggering the Miranda safeguards, i.e. Miranda rights, are "custody" and "interrogation". Custody means formal arrest or the deprivation of freedom to an extent associated with formal arrest. Interrogation means explicit questioning or actions that are reasonably likely to elicit an incriminating response.

“The person in custody must, prior to interrogation, be clearly informed that he/she has the right to remain silent, and that anything the person says will be used against that person in court; the person must be clearly informed that he/she has the right to consult with an attorney and to have that attorney present during questioning, and that, if he/she is indigent, an attorney will be provided at no cost to represent him/her.”

Justice can be created into some accounts, such as restorative and retributive justice. And that’s why human make a system in law enforcement in order to achieve the goals of justice. Restorative justice is created to restore, while retributive justice tend to make the villain pay in kind for what he/she had done, or in another word we punish them, for instance by putting them into jail, taking their rights of freedom of living with society.

RESTORE /rɪˈstɔː r / /-ˈstɔːr/ verb [ T ]
1.    to return something or someone to an earlier good condition or position
2.    If you restore a quality or ability that someone has not had for a long time, you make it possible for them to have that quality or ability again

What superheroes do is basically a retributive action by beating the criminals up.

We can say superheroes are vigilantes,

VIGILANTE /ˌvɪdʒ.ɪˈlæn.ti/ /-ˈlæn.t ̬i/ nouna person who tries in an unofficial way to prevent crime, or to catch and punish someone who has committed a crime, especially because they do not think that official organizations, such as the police, are controlling crime effectively. Vigilantes usually join together to form groups.

Yes, they do such a noble act to sacrifice for the society, but violation can’t be handled by the same violation, that’s why law is here.

So do we need superheroes? Well, the answer is yours. But If I were obliged to put a superheroes in this world. I would choose Mexico. I heard the gangster shot the police helicopter.