Sex is off course not pleasant and clean like taking a shower.
Hey, you can have sex in the shower. Or in a pool. Hot pools, outside at night, are pretty good. And who says sex is not pleasant? They r doing it rong.

And why does it have to be "clean" to be good? What exactly is so horrifying disastrous about a bit of bodily fluids? They're water-based and they wash off anyway. Why worry?
Sex is dirty as said above, I can prove that too.

Sex comes with Sexually transmitted Diseases STDs or sexually transmitted infections STIs
I have come many times, with other people no less, and have not yet acquired any STD's. Ergo, it is not definitively true that sex comes with STD's.
So its not something good as far as I know, specially if you do with strangers.
I humbly suggest that you know fuck all, and seriously need to get laid.

You guys have to give credits to abrahamic religions and many other religions, for disliking SEX.
No, I don't have to do any such thing. I can, and do, still think the Abrahamics are fucking retarded.
Old brain (animal brain), limbic system is involved during sex.

reasoning brain, new brain (prefrontal cortex) is shut during sex.
Not true. Prefrontal cortex is frequently active during sex, and thoroughly enjoying itself thank you very much. Mind you, I tend to avoid the brain dead when looking for a lover.