Elysium

Okay, I'll drop a bomb here and say this is about sexual orientation.

"No one has said what the truth should be"

Means that heteronormativity is not necessarily "the truth", but merely one aspect of many people. No one can say "X is normal, and Y is not".

"And no one decided that I'd feel this way",

Because sexual orientation is not something you choose, not yourself, not your parents, nor anyone.

"If you felt as I, would you betray yourself?"

This is quite obvious, would you not want to follow your heart, despite of what others might say?

"But, you can't deny how I feel And you can't decide for me"

That sort of thing won't change, no matter how hard you try, and it's undeniable it exists.

"No one should fear what they cannot see And no ones to blame it's just hypocrisy"

No one should be afraid of love between people, (they cannot see it, because it's an abstract thing, love, or maybe it's talking about sex, which usually happens in a private place where other people can't see) and it's a hypocritc society that which talks about freedom and won't let certain people love each other.

"It's written in your eyes And how I despise myself"

Many LGBT people end up hating themselves and fall into deep depression. It's written in "their eyes" (society's eyes) that people must be "one way", and thus those different from others dislike themselves for not fitting what is written in others' eyes.

"And it's your heart That's so wrong Mistaken You'll never know Your feathered sacred self"

And it's those who see that love other than heterosexual is evil whose hearts are "wrong", because of their hatred or fear. Using christian imagery, she states that they will never reach a sacred state, be angels or whatever, because of this intolerance, since god is all-loving and wouldn't care what love looks like, as long as it's true love.