Is it really vulgar about the Shivalinga?

It depends upon as to how one understood the spiritual meaning Union of DIVINE Feminine & Masculine energies within an individual.

The concept of Union of DIVINE Feminine & Masculine energies is ABSTRACT, in the sense that this concept can be presented pictorially or sculpturally according to One’s understanding and maturity.

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We can find the pictorial or sculptural presentation of Union of DIVINE Feminine & Masculine energies in Tantras or Puranas. However, they did not start , as generally believed, the concept of Union of DIVINE Feminine & Masculine energies of BRAHMAN.

They simply adopted this concept that was presented, in esoteric sense, in Rig Veda.

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Consider the following 2 examples from Rig Veda:

A) Union of Masculine Energy (Agni) and Feminine form of Energy (aditi) of BRAHMAN - as presented by rishi śunaśepa ājīgarti in Rig Veda 1.24.2.

B) Union of Masculine Energy (sarasvān) and Feminine form of Energy (sarasvatī) of BRAHMAN - as presented by rishi vasiṣṭha in Rig Veda Rig Veda 7.96.6.

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The examples of pictorial or sculptural presentation of the concept of Union of DIVINE Feminine & Masculine energies by Tantras or Puranas, are as follows: (Courtesy: Google photos)

a) Pictorial

Example:1

 

Example:2

 

Example:3

 

b) sculptural - tantra

 

c) Shri Lalitasahasranama stotram

The arthanarIishvara tatva was narrated as the combination of Kāmeśvara and KāmeśvarI - कामेश-बद्ध-माङ्गल्य-सूत्र-शोभित-कन्धरा - She who shines with the sacred thread in her neck tied by Kameshwara.