OP, I am going to express a dissenting view calmly and without ill-will or personal attack. It is an opinion you will seldom hear today because most people don't have the courage to say what they really think. It is an opinion that is not new or novel - rather, the view I am expressing has been the standard view for centuries.
I hope you and others have the maturity to deal with this calmly and reasonably. Here goes:
Sticking your dick up an anus is not sex. Sure it might make you dick feel good. But it's not sex.
It's abuse. Literally ab-use - misusing the rectum and the penis for purposes for which they were not intended by nature.
The rectum did not evolve to have body parts stuck up into it; it's designed to be a passage for expelling faeces. Waste matter. Crap.
There is not a biologist on earth who would dare to venture the idea that, scientifically considered, it's normal for a penis or anything else to be stuck up into the rectal cavity and abraded against the rectum wall.
Sure it can be done. It's quite possible to stick any suitably-sized body part or instrument into any bodily cavity you wish. You can choose to do it. And it's a free choice, like any other choice you make - whether to lie or tell the truth; whether to love or hate; whether to do good or to do evil. It's your choice.
And I rejoice that's it's a free choice.
To be precise: sticking a dick into an anus is a masturbatory abuse of someone else's rectum for your sexual pleasure.
You can stick your dick into a pipe and rub until you ejaculate. That's abuse, not sex.
You can stick you dick into a donkey's anus and rub until you ejaculate. It's abuse, not sex.
You can stick your dick into a hole in the wall and rub until you ejaculate. It's abuse, not sex.
You can stick your dick into a hole in a watermelon and rub until you ejaculate. It's abuse, not sex.
You can stick your dick into a mud pie and rub until you ejaculate. It's abuse, not sex.
You can stick you dick into a mouth and have the mouth suck until you ejaculate. It's abuse, not sex.
You can stick you dick into any one of ten thousand places other than a vagina, and it still doesn't rise to the noble and glorious status of sex.
Now before you go off pop, let me affirm that you are of course quite free to do what you wish with your body and with the body/bodies of consenting partner/partners. Neither the cops not the bishops will interfere, I promise.
Of course I respect your freedom to do as you wish. You are free to do right or to do wrong.
But you are only fooling yourself and playing word games when you call those actions "sex" or "sexual intercourse" or "making love" or "mating" or any such term. In all the above actions, the normal, natural, biologically-purposed, function and use of the sexual organs - the only reason why they exist as sexual organs - is not possible.
Anything other than vaginal intercourse with a real live penis is not sex. It is a misuse of the sexual organs.
It is an abuse.
Think about it carefully and ask yourself whether you want to live a life and a lifestyle that is fundamentally and intrinsically abusive. There's no getting away from that choice. It's yours to make. And it has real consequences in your life and also in society. After all, society has its origins in sex, so get sex wrong and it affects society deeply, not just you.
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Can you hear a different viewpoint without going into an apoplectic fit and spewing vitriol? I have stated the above calmly and without bile or malice or ill-will towards you or anyone else.
I hope we can keep the discussion calm and free from personal attacks and insults.