Sage Goudpada: ~ To establish the truth of Non-duality by sheer reasoning alone.+

Mango seeds cannot produce an apple tree. Similarly, a false seed collected from different sources, different Gurus sowed in the subconscious as a true seed can only produce falsehood. 

Thus, verification is necessary before sowing the seed to get the right fruit.

Accepting knowledge from different sources and different Gurus without deeper verification, is allowing all sorts of weed-growth which obstructs the realization of the self, which is beyond form, time, and space.

Katha Upanishad (1.2.5) says: ~ "Caught in the grip of ignorance, self-proclaimed experts consider themselves learned authorities. They wander about this world befooled, like the blind leading the blind."

Only a perfect understanding of 'what is what’ leads to truth realization. The truth realization is Self-realization. Self-realization is God realization.

If you are seeking truth nothing but truth then you must not get stuck to any Guru or yogi. Those who are seeking truth need not follow any Guru or any teaching.

Yoga Vasistha says:~ Self-knowledge or knowledge of truth is not had by resorting to a Guru (preceptor) nor by the study of scripture, nor by good works: it is attained only through inquiry inspired by the company of wise (Gnani). One’s inner light alone is the means, naught else. When this inner light is kept alive, it is not affected by the darkness of inertia.

There is no need to condemn Gurus, but there is need highlight how they become an obstacle in realizing the ultimate truth or Brahman.

Swami Vivekananda said: ~ “You have to grow from the inside out. None can teach you, none can make you spiritual. There is no other teacher but your own Soul.”

The Guru is useless so long as the ultimate truth is unknown, and the Guru is equally useless when the ultimate truth or Brahman has already been known.

Sage Goudpada: ~ To establish the truth of Non-duality by sheer reasoning alone. He begins by defining "What is real?" "What is unreal?" etc, because that is the right way to discuss. People must first know what they are talking about. (Mandukya Karika) : ~ Santthosh Kumaar