It's important to have your own opinions and not let others change it. It's also important to let others know that you have your own opinions, hense standing up for what you believe in.
Sticking up for what you believe in builds your self- respect because you're following through with your values. Going against what you believe in just because it's more convenient is less than admirable. Standing your ground also gains respect from others, even if they view things differently than you.
