Some suggesting that rejection of varNa amounts to rejection of Hinduism
It can also be argued that most Hindus have rejected some aspect of VarNa Vyavastha or the other, and yet remain Hindus
But notwithstanding the vyavastha, there have always been "transgressions" throughout Indian history - common enough to be discussed in Smriti texts!
The two commentaries on this Smriti - Mitakshara and Dayabhaga have had a considerable influence on Hindu law over the past several centuries
Some groupings are so complex that the commentators are not sure if it is anuloma or pratiloma!
Link is here - archive.org/details/yajnav…
The author of the Smriti (likely composed at the start of the common era) would not have discussed in such fine detail if the mixing of varNas was a rare event
And yes, notwithstanding the prejudice towards some unions relative to others, these groups were v much part of Hindu society and hardly outcastes
A class to which so many great Indian personalities belonged
Not least of which was Ugrashravas - the narrator of Mahabharata in the Naimisha forest
Society has always accommodated inter-Varna unions
That is in large measure driven by constraints of cultural compatibility, food habits, religious differences, geography, language
Nothing wrong in marrying people similar to yourself in more ways than one
But to position this as a grand vyavastha that is iron-clad is simply wrong