Some Brahmins say Buddha endorsed caste system in kannakathala sutta
In MN90, King Pasenadi asks about the caste conventions of his own society:
King Pasenadi is insightful, and his question probes deeply into freedom beyond caste:
The Buddha answers that conventions of caste do not apply to the freedom from suffering:
MN90:12.6: “In that case, I say that there is no difference between the freedom of one and the freedom of the other.
In general, the Buddha has this to say about limits:
MN43:35.2: Greed, hate, and delusion are makers of limits.
So, when presented with any caste system, the question arises: "are these limits made by greed, hate and delusion?".
In the sutta, the Buddha clearly said there is no difference among people of the different castes with respect to their practice of the Noble Eightfold Path and its results.
The fact that castes are mentioned in the sutta, is not a sign that the Buddha supported the caste system. It's simply an acknowledgement that it existed.
"Lord, if these four castes were endowed with these five factors for exertion, would there be any distinction or difference among them in that respect?"
"I tell you, great king: the difference among them would lie in the diversity of their exertion. .....
But with regard to these four castes: if they were endowed with these five factors for exertion, and they had right exertion, would there be any distinction or difference among them in that respect?"
"I tell you, great king, that there would be no difference among them with regard to the release of one and the release of another.
Kannakatthala Sutta(MN 90) (translated by Ven. Thanissaro)
The Buddha did not endorse the caste system. Instead, he taught that any person, regardless of their birth, is destined for good outcomes, if they are consummate in virtue and indulge in good practices.
In the same way,
wherever one is born
among human beings —
noble warriors, brahmans,
outcastes, or scavengers —
if one is tame,
with good practices,
consummate in virtue,
a speaker of truth,
with conscience at heart,
one who's abandoned birth & death,
completed the holy life
put down the burden,
done the task
gone beyond all dhammas,
through lack of clinging
offerings to this spotless field
bear an abundance of fruit.
In what caste was the Buddha born in?
Then Sundarika the brahmin went up to the Buddha, and said to him: “Sir, in what caste were you born?”
“Don’t ask about birth, ask about conduct.
For any wood can surely generate fire.
A steadfast sage, even though from a low class family,
is a thoroughbred checked by conscience.