To understand Maithuna and the authentic Tantrism, it is good to know some post-Vedic history of religion.
Trimurti (Sanskrit िम ू त,ि Trimūrti; “three forms”) is a concept of Hinduism that combines the three cosmic functions of creation, preservation and destruction or transformation, through the portrayal of the great gods Brahma as the Creator, Vishnu as the Sustainer, Shiva as the destroyer. The Trimurti symbolizes the origin of all divine effects in a unity, since the three aspects condition and complement each other; it represents the formless Brahman and expresses the creative, sustaining and destroying aspects of this supreme being.

According to this, whoever is regarded as the highest being is distinguished from Brahmins, Vishnuites and Shaivites. There have never been many Brahmans, Vishnuites and Shivaites are the real bulk of Hindus. It is estimated that of the Hindus today, one third worship Vishnu and two thirds Shiva. The best works of Indian literature, such as the poems of Kalidasa (literally: Servant of the Goddess Kali) and the richest sanctuaries of the land, such as the Temple of Somnath, are dedicated to Shiva.
The significant role that Shiva played and plays in the religious life of the Hindus meant that his followers soon attributed to him a greater scope: nothing, they argued, could arise from nothing; Creation is therefore only the reconstruction of the destroyed; and destruction is therefore an integral part of reconstruction.
So it happens that the god later got not only the role of the exterminator, but also that of the restorer. The symbol of his creative power became his phallus …

Shiva’s lingam is of immense size. In the temples dedicated to Shiva, there is a columnar stone stump in the Holy of Holies that rises from the center of a stone subsoil with a circular border and a tube-shaped opening. This union of lingam and yoni symbolizes the world- preserving divine sexual act.
These symbols have nothing disreputable and are worshiped daily by millions of Indians. Some probably do not even know their true meaning. And I’m not talking about Tantrics here, but believing Hindus ….

Notwithstanding their division into Brahmins, Vishnuks and Shivaites, all Hindus agree on one essential point: the driving force of the world is always feminine. Accordingly, the gods also possess Brahman, Vishnu and Shiva as such passive characters. Only their marriage to the goddess-worshiped energy – Shakti – gives them activity.
And you see, from here takes Shaktist Tantrism, the mystical current of Hinduism, which is demonized by many devout Hindus, their output …

P.S. Do you know how Shiva should have destroyed ??
Dancing wild !!
When Shakti then showed him the gentle Tandava, the destroyer became a creator … 😉