Tantra - physical vs spiritual

Based on online definition:

Look at these spiritual beings!

"Tantra is a Sanskrit word that means 'woven together.' Hindu and Buddhist meditation practitioners use sexual union as a metaphor for weaving together the physical and the spiritual: weaving man to woman, and humanity to the divine. The purpose is to become one with God."

Oh please, give me a break! Admit it, it's just physical! There might be some emotional and spiritual touch but, sex is sex. The so called "divine" or "spiritual" part is way too far fetched. To me, it only shows humans' lack of confidence in pursuing physical pleasure.

Spirituality

The reason that we humans are so obsessed with our spirituality or mentality - its pain and joy, or its power, is precisely because of our completely helpless physical vulnerability. 

Why there are so many"techniques" about sex in Taoism?

Unlike any other Chinese ancient philosophy, Taoism teaches many techniques about sexual practice. By my understanding, this is because Taoism focuses mostly on human's physical health. Ok, don't get me wrong, it is not that Taoists don't care about spiritual matter, but they believe that physical health is the fundation of our mental health.
Well, did Lao zhi really said that? I am not sure... but this is how I understand Tao.
By the way, I am personally not so crazy about this part of Taoism. I think if you exercise often and eat well, you will have awesome sex!