Why do we have to have sex if we don't want to?

That's a really good question. I'm curious too.

Who are "they"?
What's it any of their business?

"Wouldn't the same logic apply to them, for example if they're straight and have no desires to have sex with the same sex, "you don't know until you try"?"

No, not really. The difference being the lack of sexual attraction. They are probably assuming you are sexually attracted to some type of person/thing, just choosing to not act on it. They're not necessarily expecting you to have sex with someone/something you aren't attracted to whereas in your example you are suggesting that they should. They could be wrong and you might not feel any sexual attraction, I'm not saying they are right in assuming you do, I am just explaining where they are probably coming from when they say that to you.

Stop telling people this if the response bothers you so much.

You don't have to. People are idiots.

I really do not understand your question here?

Are you asking should we all try and have gay sex?

Are you asking should we consent to sex even if we do not feel in the mood?

Are you asking should we consider letting somebody of the same sex have intercourse with us?

With what "thing" should we have sex? Is it an object like a dildo or is it a animate object?

You really need to be a little more specific when you post something!

For the record i would just like to say "Don`t knock it until you have tried it!"