If all Paths are equal then why was the Sikh religion started?

It is a ‘totally false’ argument that Sikhism believes all paths lead to the same goal and thus all religions are equal. From its very inception, Gurmat (the Guru’s Path) has been declared a unique and distinct path. Bhai Gurdaas Ji writes:

ਮਾਰਿਆ ਸਿੱਕਾ ਜਗਤ ਵਿਚ ਨਾਨਕ ਨਿਰਮਲ ਪੰਥ ਚਲਾਯਾ॥
“In the world, Guru Nanak Sahib Ji established the authority (of his doctrines) and started a Path (of religion), devoid of any impurity.”
(Vaar 1, Pauree 45 – Bhai Gurdaas Ji)

The claim that all paths lead to the same goal is covered in Bhai Sahib Randheer Singh Ji’s book ‘Anhad Shabad Dasam Duar – Open discussion of unstruck ethereal music at tenth door of abode-divine’, pages 46-47:

“The Liberation-state of Gurmat is unique and different in concept from other religious faiths. Liberation is not the mere ending-up of the human body or just an escapement of the soul from its bodily cage. Some envisage liberation as riddance from afflictions associated with the human body. They believe liberation is unattainable as so long as the soul is caged within the human body. Others identify liberation as the fulfilment of their desires to abide in a heavenly abode. However, this kind of liberation falls very short compared to the Gurmat concept of liberation. Liberation is not the banishment of imagined pain and sorrow, nor can it be described as the disassociation of the soul-being from materialism. Yogic faith conceives liberation as empty consciousness through meditational practices that bear no semblance to the Gurmat concept. Vedantic faith believes in the removal of duality to arrive at oneness with The Absolute, in order to be liberated. Buddhism believes liberation to be a state of total renunciation of desire and negative thought – Nirvaana. Jainism considers that non-violence and non-killing leads to liberation. Mere escape from transmigration is not the essence of True Liberation….
Gurmat considers the above listed forms of liberation as halfway and incomplete. The swan-bird Gurmukhs who are blessed with Divine Enlightenment reject all these forms. They merge with The Divine Immaculate Light whilst living; they envision The Glorious Lord in full Divine Splendour.
Gurmukhs are sustained by the nourishment of Naam-Divine, while they behold The Lord at all times. They find True Liberation within this Love-Divine… Their Liberation lies in the sole occupation of Naam-Devotion, in accordance with Gurmat. This supreme state is reached through complete dedication, when one takes refuge within The Guru… what is not sought is a form of liberation devoid of God-Realisation.”

If we use this viewpoint to analyse some mainstream schools of thought, we may reach the following conclusions:

In Hindu or Vedantic traditions, Liberation = various states according to different schools i.e. freedom from transmigration, realisation of self as God (Sohang) etc.
In Buddhism, Liberation = realisation of the nature of self/ escape from desires/ Nirvaana.
In Judaism, Christianity, and Islam, Liberation = heavenly abode/ paradise
In Sikhi, Liberation = absorption into Vaheguru/Naam, the destruction of self/ego, the merging of Aatma (soul) into ParAatma (Universal Soul) – all of which can only be achieved through complete dedication to The Guru’s Teachings.

The concept of equality exemplified by Sikhi is not the result of a debate concerning which paths are more (or less) efficient and ultimately productive; equality is not based upon such rational discussions or language games. The Sikhi concept of equality is an inward and outward acceptance of all and seeing everyone as a soul rather than religious labels, which results directly from the practice of Sri Guru Granth Sahib jee’s teachings.
When it comes to true enlightenment, or liberation, Guru jee is very clear about its unique nature and definition within Gurmat; and in doing so we are taught who and what The True Teacher is.
Sri Guru Granth Sahib jee over and over stresses the importance of “Gurmat Naam”. Without Gurmat Naam no one can merge in Vaheguru or reach ‘Sach Khand’ (the spiritual state of Truth). In the House of Guru Nanak only Naam is found, the only tool to experience and merge into God.

ਏਹੁ ਅਹੇਰਾ ਕੀਨੋ ਦਾਨੁ ॥
ਨਾਨਕ ਕੈ ਘਰਿ ਕੇਵਲ ਨਾਮੁ ॥੪॥੪॥
“God has given this gift. Nanak’s home is filled with only Naam, the Name of Vaheguru. ||4||4||
(Ang 1136)

Without Naam, no one can be liberated and merge with God. Gurbani is clear about this fact:
ਸਭਿ ਸੁਖ ਮੁਕਤਿ ਨਾਮ ਧੁਨਿ ਬਾਣੀ ਸਚੁ ਨਾਮੁ ਉਰ ਧਾਰੀ ॥
ਨਾਮ ਬਿਨਾ ਨਹੀ ਛੂਟਸਿ ਨਾਨਕ ਸਾਚੀ ਤਰੁ ਤੂ ਤਾਰੀ ॥੯॥੭॥
“Those enshrined the True Name within their heart, those within is the flowing current of Naam, and those whose consciousness is attached to the vibrations of the Guru’s Baani obtain all comforts and liberation from Maya (the illusionary world). O Nanak! Without the Naam, no one is saved; You too swim across to the other side this true way in which there no chance of drowning. ||9||7||”
(Ang 1013)

Sikhi is unique by the fact that it does not condemn others to Hell or say if you are not Sikh you are eternally damned. Rather a Sikh prays at least twice daily for “Sarbat Da Bhallaa”, meaning the good and prosperity of all Humanity regardless of religion, belief or faith.

ਨਾਨਕ ਨਾਮ ਚੜਦੀ ਕਲਾ। ਤੇਰੇ. ਭਾਣੇ ਸਰਬੱਤ ਦਾ ਭਲਾ।
“May the Divine-Name preached by Nanak be exalted. May all prosper and be blessed within Your Will.”
(Daily Sikh Ardaas)
All faiths will get what they work towards. Guru Nanak Sahib jee is the only True Guru who has preached Naam, and given Gurmat-Naam. Only Gurmat has a concept such as Sach Khand and God-Realisation in such a clear way. Thus, Gurmat is the only path to Sach Khand, i.e. merging with God.