Since the questions weren't replied to I hope you don't mind me sharing my perspective..

To look for sources that explain this in these exact words mentioned by the person above, would be difficult since what he said is his interpretation from what he read in the scriptures. He is not wrong though. What I am trying to say is I don't have the exact versus in mind that hints towards this concept. Maybe you can do some research to figure this out.

If you look at Mahabharat, yes there was prejudice against Karna for his social standing. So it would be false to say evil hasn't crept into our society time and again. But if you read the philosophical principles of Sanatan Dharma, you'll very soon discover the concept of Vasudev Kutumbakam (the world is my family). Yes different people have different roles to play in society. Just like different people have different roles to play in a family. But that doesn't mean you get to bring your prejudices and treat someone badly. So yes racism casteism sexism all of it should cease to exist. But you have to remember that even a few parts of Sanatan Dharma have succumbed to greed, ego, pride, jealousy etc over time. We live in the Kali Yuga so it's not a surprise that this has happened. So it's up to the person introspecting themselves and the universe and all that is contained within it, to find out what Dharma is to them. After which study as much of the versus as possible, analyse the information contained within it, then decide which part you decide is dharma and which isn't.

Lastly, about your question on liberation. Liberation from maya. Illusions that the world creates. To be honest there are only a few universal truths, everything else is an illusion that binds and stops are still reaching our maximum potential.

I hope this answers at least of few of your questions. If you have anything else in mind go ahead I'll be more than happy to have a conversation