People like to talk.
And people will talk about you. It might be behind your back or to your face.
Some people are not your friends and are actively trying to take you down. It makes people feel bigger and better if they destroy you. Everyone wants the biggest building but some people do it buy tearing down all the buildings around them.
People will grandstand and look down on on you to make themselves feel superior.
Not everyone has your best interest in mind. They are trying to push their own agenda instead of lifting up yours.
In all these cases it is not only ok to fight back but it is your moral duty to stand up for what you believe in. You must hold your ground and hit back twice as hard. Do not let other people take advantage of you. Do not tolerate anything less than you deserve.