The 18-year-old "Neighbors 2: Sorority Rising" actress, who is close to all her four siblings, was in middle school when her brothers Trevor and Colin came out as gay, reported People magazine.
"At 11, you're incredibly observant and realising what society is, and who you are, and people are kissing boys or girls for the first time, and you're really starting to understand what sexuality is.
"The problem is we live in a society where we have to say the words, 'I'm coming out.' No one should care what your sexual orientation is, what colour your skin is, or if you're a man or a woman," Moretz said.
"People would call them the F-word, and I would get so angry. It was really hard to see my brothers be hated on or bullied, so I stood up for them. We shouldn't be using these terms to create more labels and segregate us further apart than we already are."
Moretz said, from a young age she "was motivated to fight for gay rights, women's rights, minority rights - all human rights." And now when she is famous, she hopes to use her visibility to continue fighting for equality.