Ethical thinking on Plato's Republic

After reading the PDF on Plato's republic, I do not agree with Thrasymacus when he says that justice "is nothing other than the advantage of the stronger" because of my interpretations of justice. To me, I feel like justice is meant for everyone no matter how strong or weak, brave or cowardly someone is. Just because you give a king a sword, doesn't mean they are the strongest in the kingdom. To me, justice is a mindset that we have when we see something wrong and want to make it right. In other words, doing the right thing. Whether or not we choose to take action is entirely up to that person. But I also can agree with him in some ways because it is sometimes true when people look up to someone who is just, someone who has certain qualities that others lack which can lead to leadership and trust. Someone people can look up to. It can be enthusiasm, charisma or even bravery. For example, someone who is very talkative, outgoing and wise is most likely to have more friends than someone who is shy and quiet. But justice is not having an advantage over others, it's more of an acquired trait that we can choose to act upon when something seems wrong such as helping someone against a bully. 

Having the ability to do something does not make it morally acceptable depending on the situation. For example, just because I know how to pick locks, doesn't mean I'm going to go around picking at every locked door I find. But deciding to choose whether you should do something is entirely up to you. Another example would be if your best friend just told you they murdered someone and needed a place to hide. You are now in a situation where you can decide whether to turn them in or not. But just because you have the ability to hide them from the police does not mean that you should. Maybe the person they murdered deserved it, maybe they didn't. The problem is that sometimes what we think is morally acceptable is not to others. They could be from other cultures that have customs that are different from ours. For example the thing we discussed about kissing on the cheeks when greeting someone. It may seem weird to us and maybe feel uncomfortable from it, but to them it is done all the time and is normal. There are tribes around the world that accept cannibalism, while we are born and raised not to eat other humans. Going back to the original question, it's just a matter of knowing if having the ability to do something is right or wrong.

I kinda rushed this seeing as I do not really go on the internet often and have little time to use it but if this needs more revising please drop a comment down below.