Why do some people think you'll go to hell just for being gay? Like can't you have an opinion over who you want to love??

You ask:  Like can't you have an opinion over who you want to love??

So, you imply being gay is a choice you can make---do you believe that?

people misinterpret the bible, thinking that being gay is a sin. Also, people (christians) throw their beliefs on others and it sucks. I personally have experienced hate while i was at a private christian school because i was gay. The only thing making people believe that your sexual orientation is a sin is beliefs and ignorance.

Some would say that being gay is a demon that can be cast out.

Because they pick and choose what Bible verses to believe .. And the Old Testament in Leviticus says that homosexuality is a sin deserving death. 

Of course, it also says not to eat certain things or wear clothing made of multiple materials ... Which they conveniently ignore.

B cuz the Bible says in 1st Chorinthians 6:9 that homosexuals will not enter the kingdom of God

Your sexual orientation has nothing to do with hell or heaven because both don't exist. You live right and do whatever makes you happy without hurting other. Hell or heaven created by you with the kind of living you do.

If you are referring to one of the three monothestic religions the reason it was frowned on was because homosexuality was often seen in temple prostitution to other gods such as Ishtar. It is the homosexual act that is "taboo"often translated as an abomination in the bible.

It is also noted that when man and woman join in love they become one flesh.

In Genesis 2:22 Woman was made from man's rib/side. In Jewish Midrash Adam or Adama was both male and female androgenous.

The LORD God fashioned into a woman the rib which He had taken from the man, and brought her to the man. The man said, "This is now bone of my bones, And flesh of my flesh; She shall be called Woman, Because she was taken out of Man." For this reason a man shall leave his father and his mother, and be joined to his wife; and they shall become one flesh.

http://thetorah.com/the-making-of-adam/

https://en.m.wikipedia.org/wiki/Apocalypse_of_Adam

Genesis 2:24

Therefore shall a man leave his father and his mother, and shall cleave unto his wife: And they shall be one flesh.

Mark 10:8

And they twain shall be one flesh: So then they are no more twain, but one flesh.

Cor 6:16

Or do you not know that the one who joins himself to a prostitute is one body with her? For He says, "THE TWO SHALL BECOME ONE FLESH."

Eph 5:28 - 29

So husbands ought also to love their own wives as their own bodies. He who loves his own wife loves himself; for no one ever hated his own flesh, but nourishes and cherishes it, just as Christ also does the church,

Even in tantric sex the union must be between man and woman which is eastern belief.

Opinions seem to communicate Choice. Can you choose who you fall in love with? When did I choose to be heterosexual . . .

That being said, Most holy Scriptures have a problem with Same sex relationships. It was either misunderstood be the original writers, or Simply meant that the union would not produce fresh off-spring to Indoctrinate and keep the religion moving forward.

No Gods are required for men to produce texts to control the masses by fear of an invisible eternal punishment.

Lucky for them I guess . . . Becaue no Gods could be found.

Q "Why do some people think you'll go to hell just for being gay? Like can't you have an opinion over who you want to love??"

Let's start with what you have boiled it down to: "can't you have an opinion over who you want to love??"

If, say, it's just a handful of you on an Island by yourselves where no rules apply [extremely impractical, of course] then perhaps you cannot only have an opinion over who you want to love, be it your neighbour's wife, daughter or son, [or even all three] or what you want to smoke or snort but you can go ahead and act on that opinion.

However, if you want to organise yourselves into a smoothly functioning society then you will need rules or laws for the wellbeing and future of your society. Even in the most liberal of societies you will have limits beyond which you cannot put your opinions into practice. In the more conservative ones you might be taken to task for just expressing certain opinions, let alone acting upon them.

If a society enacts a certain law it will stipulate what it considers appropriate punishment for any breach of the law. Where a law accepted by a society comes from, or is claimed to come from, an external source [federal, international or "God"] then that source will most likely have stipulated what it considers appropriate punishment for any breach of the law [be it imprisonment, lashes, stoning or a spell in hell, or any combination thereof].

I'm a Catholic, but I have to say that I don't believe in a lot of things that the Church teaches.

First, I believe that an individual's relationship with God is between that person and God, and nobody else.  This is why I do not believe in confession.  First of all, God will know what sins I have committed, and he will know if I am repentant.  What reason is there to go and confess your transgressions to another human being?

As far as going to Hell when you die, I believe that only people who are evil and have committed evil deeds while they were alive wind up going to Hell.

Even if you never went to a mass in your entire life, but you are a good person with a kind heart, then you are going to go to Heaven.

Being gay certainly does NOT make you evil.  You are allowed to love who you want to love.  If that happens to be another man or another woman, or both, so be it.

I firmly believe that what determines where you go in the afterlife depends fully on how you treated other living things when you were on Earth. 

If you were malicious and you constantly hurt others and aimed to destroy the happiness of others, then you will reap what you sow.