It seems misleading to call Smriti "scripture" in the sense that's understood in the West. They're texts/literature connected to religion in some loose sense but encompass all sorts of subjects, are full of contradictory claims, and were never seen as exempt from criticism and revision, particularly over long spans of time and changing social customs. Nobody here is denying that some Hindus have historically endorsed and practiced caste discrimination; the meaningful debate is whether these things are representative of Hinduism itself, as in the religion and belief system.
Then Ramayana and Mahabharata aren't scriptures, too.
Smritis are definitely scripture.
And yes, there were dissenters.
And no, not of only some Hindus, the casteism was systematic.
I have reletives in a small town, and my uncle remembers that in every wedding receptions and funerals brahmins ate first and no one else was allowed to eat together with them.
Only after brahmins had finished, people from other castes could begin eating.
