There are sometimes we fear the judgment of others or close our mouths even when we are right.  We rather ignore the wrongdoing to us thinking they will change and things will get better only to be disappointed every time when this could have been avoided by telling them directly what we think or at the very least not ignoring their actions. In the end, we only managed to make them think highly of themself as if they can do whatever they, please. This habit has many consequences that affect the way we interact with others. Bellow, I will quote some of them.

they will take your silence as consent.

And this is bad for you. When you don't tell people what you think and remain quiet they might take advantage of it to do to you what they want. Some won't miss any chance to try to hurt you in case they know you won't respond, which is fine for them. In the end, being quiet isn't helping you but contributing to your suffering. 

But when you say enough is enough and make it clear that you don't like the way they are behaving around you arent only liberating yourself by not accepting the nonsense but making it clear that you won't stand their action any longer. This can b a red flag for them.

Some might change and behave. It will make it possible for you to connect with the right people 

when you say what you think, people who share your view can easily find you and connect to you. 

You won't be at ease at all

You cant be at ease when someone is doing something you don't like with you, and it's not by remaining silent that it will change.

It's also possible to avoid a misunderstanding when you express your mind. A lack of understanding of one another just causes that. This makes it almost impossible to be with them.

Expressing yourself won't only change others' views about you. but make it easier to avoid misunderstanding.

People won't include you in their decision

No one will include you in their decision when they barely know what you think. So it's again very important for you to be open and strong.

Now Some will be hard on you and try to bully you, it's for you not to accept their nonsense, you can either cut them from your life or report them if they won't stop. The world is full of billions of people, cutting some out won't be the end of everything. This will also allow you to spend your time with the people who are worth it.