Why Slander then? A Sikh of the Guru is a Saint-Soldier and pooran Sat-Guru?

Guru Gobind Singh Ji gave every Khalsa Sikh male and female a title of Sat-Guru when He said, Khalsa mera sat-guru poora. And, yet many of us fail to recognize that infinite divinity in each one of us and act with malice, anger, and hatred towards others, slander and talk behind their back. We exploit each other for material things.

ਧਨਾਸਰੀ ਮਹਲਾ ੫ ॥ धनासरी महला ५ ॥ Dhanāsrī mėhlā 5. Dhanaasaree, Fifth Mehl:
ਹਰਿ ਹਰਿ ਲੀਨੇ ਸੰਤ ਉਬਾਰਿ ॥ हरि हरि लीने संत उबारि ॥ Har har līne sant ubār.
The Lord saves His Saints.
ਹਰਿ ਕੇ ਦਾਸ ਕੀ ਚਿਤਵੈ ਬੁਰਿਆਈ ਤਿਸ ਹੀ ਕਉ ਫਿਰਿ ਮਾਰਿ ॥੧॥ ਰਹਾਉ ॥ हरि के दास की चितवै बुरिआई तिस ही कउ फिरि मारि ॥१॥ रहाउ ॥ Har ke dās kī chitvai buri▫ā▫ī tis hī ka▫o fir mār. 1 rahā▫o.
One who wishes misfortune upon the Lord's slaves, shall be destroyed by the Lord eventually. 1Pause
ਜਨ ਕਾ ਆਪਿ ਸਹਾਈ ਹੋਆ ਨਿੰਦਕ ਭਾਗੇ ਹਾਰਿ ॥ जन का आपि सहाई होआ निंदक भागे हारि ॥ Jan kā āp sahā▫ī ho▫ā nindak bhāge hār.
He Himself is the help and support of His humble servants; He defeats the slanderers, and chases them away.
ਭ੍ਰਮਤ ਭ੍ਰਮਤ ਊਹਾਂ ਹੀ ਮੂਏ ਬਾਹੁੜਿ ਗ੍ਰਿਹਿ ਨ ਮੰਝਾਰਿ ॥੧॥ भ्रमत भ्रमत ऊहां ही मूए बाहुड़ि ग्रिहि न मंझारि ॥१॥ Bharmat bharmat ūhāʼn hī mū▫e bāhur garihi na manjhār. 1
Wandering around aimlessly, they die out there; they never return to their homes again. 1
ਨਾਨਕ ਸਰਣਿ ਪਰਿਓ ਦੁਖ ਭੰਜਨ ਗੁਨ ਗਾਵੈ ਸਦਾ ਅਪਾਰਿ ॥ नानक सरणि परिओ दुख भंजन गुन गावै सदा अपारि ॥ Nānak saran pari▫o dukh bhanjan gun gāvai sadā apār.
Nanak seeks the Sanctuary of the Destroyer of pain; he sings the Glorious Praises of the infinite Lord forever.
ਨਿੰਦਕ ਕਾ ਮੁਖੁ ਕਾਲਾ ਹੋਆ ਦੀਨ ਦੁਨੀਆ ਕੈ ਦਰਬਾਰਿ ॥੨॥੧੫॥ निंदक का मुखु काला होआ दीन दुनीआ कै दरबारि ॥२॥१५॥ Nindak kā mukh kālā ho▫ā dīn dunī▫ā kai darbār. 215
The faces of the slanderers are blackened in the courts of this world, and the world beyond. 215