that pair of comments seem to me in OP to be callous
if one gets frustrated and upset when another doesn't immediately concede their opinion or behavior then perhaps they should not teach dhamma
my impression is the buddha inclined not to teach because of two very deep points in the dhamma, not because it would be a waste of time or some other apathy
here is the buddha teaching a couple of boys he apparently happened upon:
Then early in the morning the Blessed One adjusted his under robe and — carrying his bowl & robes — went into Sāvatthī for alms. He saw the large number of boys on the road between Sāvatthī & Jeta's Grove catching little fish. Seeing them, he went up to them and, on arrival, said to them, "Boys, do you fear pain? Do you dislike pain?"
https://www.accesstoinsight.org/tipitak ... .than.html
and here is the buddha talking to someone who is doomed to the lower realms:
Then, Bhaggava, Sunakkhatta, the Licchavi, came to call on me, and saluting, he sat down beside me.
To him, so sitting, I said: ‘What think you of it, Sunakkhatta?
Has it fared with Pāṭika’s son as I declared unto you, and not otherwise?’
‘It has fared with him even as the lord, the Exalted One, declared unto me, and not otherwise.’
‘What think you of it, Sunakkhatta?
If it be even so, has a mystic wonder through superhuman gifts been wrought, or has none been wrought?’
‘Verily, Sir, it being even so, a mystic wonder through superhuman gifts has been wrought indeed.’
‘Even so do you, you foolish man say of me working mystic wonders by superhuman gifts: “The lord, the Exalted One, works no mystic wonder with his superhuman gifts.”
Behold, O foolish man, how far you have committed yourself.’
Thus, Bhaggava, did Sunakkhatta the Licchavi, addressed by me, depart from this Doctrine and Discipline, as one doomed to disaster and to purgatory.
https://legacy.suttacentral.net/en/dn24
theres also prince/king ajatasattu who wouldve attained stream entry hearing the buddha if he had not previously killed his father
https://www.accesstoinsight.org/tipitak ... .than.html (the last few lines)
btw, kesi sutta says
But if a tamable person doesn't submit either to a mild training or to a harsh training or to a mild & harsh training, then the Tathagata doesn't regard him as being worth speaking to or admonishing. His knowledgeable fellows in the holy life don't regard him as being worth speaking to or admonishing. This is what it means to be totally destroyed in the Doctrine & Discipline, when the Tathagata doesn't regard one as being worth speaking to or admonishing, and one's knowledgeable fellows in the holy life don't regard one as being worth speaking to or admonishing."
https://www.accesstoinsight.org/tipitak ... .than.html
for one, i dont think many of us have knowledge of seeing other beings faring according to their kamma and so we dont have the knowing to declare someone a fool or someone wise, just our own blind guesses. there are many other heretics that the buddha talked to, i would just have to be diligent about linking them
In the same way, if anyone were to say, 'Suppose that a brahman or contemplative were to arrive at a skillful doctrine. Having arrived at a skillful doctrine, he should not declare it to anyone else, for what can one person do for another? It would be just the same as if, having cut through an old bond, one were to make another new bond. I say that such a thing is an evil, greedy deed, for what can one person do for another?' — he, speaking in this way, would be a creator of obstacles for those children of good family who, coming to the doctrine & discipline revealed by the Tathagata, attain the sort of grand distinction where they attain the fruit of stream-entry, the fruit of once-returning, the fruit of non-returning, the fruit of arahantship; and for those who ripen deva wombs for the sake of bringing about the deva state. Being a creator of obstacles, he would not be sympathetic for their welfare. In one not sympathetic for their welfare, the mind would be established in animosity for them. When the mind is established in animosity, there is wrong view. For one of wrong view, I tell you, there is one of two destinations: either hell or the animal womb.
https://www.accesstoinsight.org/tipitak ... .than.html
this sutta speaks for itself, no?
“Then the potter Ghaṭīkāra seized the brahmin student Jotipāla by the belt and said: ‘My dear Jotipāla, there is the monastery of the Blessed One Kassapa, accomplished and fully enlightened, quite nearby. Let us go and see the Blessed One Kassapa, accomplished and fully enlightened. I hold that it is good to see that Blessed One, accomplished and fully enlightened.’ Then the brahmin student Jotipāla undid his belt and said: ‘Enough, my dear Ghaṭīkāra, what is the use of seeing that bald-pated recluse?’
“Then, when the brahmin student Jotipāla had washed his head, the potter Ghaṭīkāra seized him by the hair and said: ‘My dear Jotipāla, there is the monastery of the Blessed One Kassapa, accomplished and fully enlightened, quite nearby. Let us go and see the Blessed One Kassapa, accomplished and fully enlightened. I hold that it is good to see that Blessed One, accomplished and fully enlightened.’
“Then the brahmin student Jotipāla thought: ‘It is wonderful, it is marvellous that this potter Ghaṭīkāra, who is of a different birth, should presume to seize me by the hair when we have washed our heads! Surely this can be no simple matter.’ And he said to the potter Ghaṭīkāra: ‘You go as far as this, my dear Ghaṭīkāra?’ ― ‘I go as far as this, my dear Jotipāla; for so much do I hold that it is good to see that Blessed One, accomplished and fully enlightened!’ ― ‘Then, my dear Ghaṭīkāra, let go of me. Let us visit him.’
http://www.yellowrobe.com/component/con ... otter.html
in this sutta, jotipāla is the buddha-to-be gotama in a past life. he ordains under kassapa buddha as a result of ghatikara's compassion for him
and this right here ought to be pinned somewhere in the sub-forum:
Go forth, o bhikkhus, for the good of the many, for the happiness of the many, out of compassion for the world, for the benefit, for the good, for the happiness of gods and men. Let not two go by one way. Preach the doctrine that is beautiful in its beginning, beautiful in its middle, and beautiful in its ending. Declare the holy life in its purity, completely both in the spirit and the letter. ~ Mahavagga, Vinaya Pitaka.
http://www.parami.org/dhammaduta/
so while one's exposition of dhamma will probably be flawed without a noble attainment, i think it's our duty to try to instruct, exhort, persuade, and so on
otherwise, we're feeding ill will or slackness, which hurts our own growth in dhamma
Good is the sight of those who’ve practised well;
Doubt is cut off, and intelligence grows.
Even a fool becomes wise;
Therefore meeting with such people is good.
https://suttacentral.net/thag1.75/en/sujato-walton
even if we dont convert someone we may plant a seed in their mind, we may correct our own wrong view, we may benefit in our understanding by teaching, such as ven khema did
https://www.accesstoinsight.org/tipitak ... .than.html, nothing could be lost, only gained. tolerate slander and abuse like the earth would tolerate it, with complete equanimity. remove your personal feelings and rejoice in the dhamma while it's still in the world