AN 5.191 Why did the Buddha categorically consider the latter brahmans to be inferior?

 (A sutta from AN I believe)

“In the past, brahman males mated only with brahman females and not
with non-brahman females. At present, brahman males mate with
brahman females and with non-brahman females. At present, male dogs
mate only with female dogs and not with female non-dogs. This is the first
ancient brahmanical tradition that is now observed among dogs but not
among brahmans.… In the past, brahmans did not make a stash of wealth,
grain, silver, or gold. At present, brahmans make stashes of wealth, grain,
silver, & gold. At present, dogs do not make a stash of wealth, grain, silver,
or gold. This is the fourth ancient brahmanical tradition that is now
observed among dogs but not among brahmans.”

A friend asked me:

Why did the Buddha categorically consider the latter brahmans to be inferior?  I thought the latter brahman males may be more evolved as some of them may have overcome their prejudices to not judge people based on castes but on characters.  And why are brahmans categorically considered superior just because they don't store wealth?  You can have brahmans with filth in their minds and not accumulate physical wealth.  And you can have brahmans who accumulate wealth and behave with great nobility.  

The satire seems out of character for the Buddha. 

and a follow up question after my original answer:

It still doesn't address that the Buddha was not praising the former for not mating but mating with their own caste.

My response part 1 (satire out of character?):

Why do you think it's out of character for the Buddha to use satire? There are plenty of suttas where the Buddha makes fun of heterodox traditions with wrong views. 

Just to give two examples off the top of my head:

MN 78 Samaṇamuṇḍika

• • (Uggāhamāna's invincible ascetic— no bad body action, word, thought, livelihood)
  • (Buddha makes fun of him, compare to baby)

a leader in a  group of 300 brahmans, describes what they consider the ideal qualities of an ascetic.  

(Buddha makes fun of him, compare to baby)

Evaṃ vutte, bhagavā pañcakaṅgaṃ thapatiṃ etadavoca:	When he had spoken, the Buddha said to him:
“evaṃ sante kho, thapati, daharo kumāro mando uttānaseyyako sampannakusalo bhavissati paramakusalo uttamapattipatto samaṇo ayojjho, yathā uggāhamānassa paribbājakassa samaṇamuṇḍikāputtassa vacanaṃ.	“Master builder, if what Uggāhamāna says is true, a little baby boy is an invincible ascetic—accomplished in the skillful, excelling in the skillful, attained to the highest attainment.
Daharassa hi, thapati, kumārassa mandassa uttānaseyyakassa kāyotipi na hoti, kuto pana kāyena pāpakammaṃ karissati, aññatra phanditamattā.	For a little baby doesn’t even have a concept of ‘a body’, so how could they possibly do a bad deed with their body, apart from just wriggling?
Daharassa hi, thapati, kumārassa mandassa uttānaseyyakassa vācātipi na hoti, kuto pana pāpakaṃ vācaṃ bhāsissati, aññatra roditamattā.	And a little baby doesn’t even have a concept of ‘speech’, so how could they possibly speak bad words, apart from just crying?

And in MN 152, Buddha makes fun of another brahman's ideal ascetic, comparing that to a blind and deaf person being ideal. 

• MN 152 Indriya-bhāvanā
  • (brahman Parasiri teaching of indriya ridiculed )
    • 1st type: unexcelled development of faculties
    • 2nd type: trainee
    • 3rd type: noble one with developed faculties
    • conclusion

MN 152 Indriya-bhāvanā

MN 152 Indriya-bhāvanā-sutta	MN 152 Indriyabhāvanā Sutta: The Development of the Faculties
Evaṃ me sutaṃ— ekaṃ samayaṃ bhagavā gajaṅgalāyaṃ viharati suveḷuvane.	I have heard that on one occasion the Blessed One was staying among the Kajjangalas in the Bamboo Grove.
Atha kho uttaro māṇavo pārāsiviyantevāsī yena bhagavā tenupasaṅkami;	Then the young brahman Uttara, a student of Parasiri[1] went to the Blessed One and,
upasaṅkamitvā bhagavatā saddhiṃ sammodi.	on arrival, exchanged friendly greetings & courtesies.
Sammodanīyaṃ kathaṃ sāraṇīyaṃ vītisāretvā ekamantaṃ nisīdi.	After this exchange of courteous greetings he sat to one side.
Ekamantaṃ nisinnaṃ kho uttaraṃ māṇavaṃ pārāsiviyantevāsiṃ bhagavā etadavoca:	As he was sitting there, the Blessed One said to him:

(brahman Parasiri teaching of indriya ridiculed )

“deseti, uttara, pārāsiviyo brāhmaṇo sāvakānaṃ indriyabhāvanan”ti?	"Uttara, does the brahman Parasiri teach his followers the development of the faculties?"
“Deseti, bho gotama, pārāsiviyo brāhmaṇo sāvakānaṃ indriyabhāvanan”ti.	Yes, master Gotama, he does.
“Yathā kathaṃ pana, uttara, deseti pārāsiviyo brāhmaṇo sāvakānaṃ indriyabhāvanan”ti?	And how does he teach his followers the development of the faculties?
“Idha, bho gotama, cakkhunā rūpaṃ na passati, sotena saddaṃ na suṇāti—	"There is the case where one does not see forms with the eye, or hear sounds with the ear [in a trance of non-perception].
evaṃ kho, bho gotama, deseti pārāsiviyo brāhmaṇo sāvakānaṃ indriyabhāvanan”ti.	That's how the brahman Parasiri teaches his followers the development of the faculties."
“Evaṃ sante kho, uttara, andho bhāvitindriyo bhavissati, badhiro bhāvitindriyo bhavissati;	"That being the case, Uttara, then a blind person will have developed faculties, and a deaf person will have developed faculties,
yathā pārāsiviyassa brāhmaṇassa vacanaṃ.	according to the words of the brahman Parasiri.

Many people have the wrong impression of how a Buddha or arahant should behave, because they're projecting dependently arisen, impermanent arbitrary modern cultural norms on to what they believe an enlightened being should be. The Buddha spoke the truth, but he did it selectively, and only when he knew it wouldn't do harm. So the fact that he made fun of heterodox wrong views just means the cultural norms for his time meant they wouldn't interpret it as inappropriate or offensive. 

My response to friend's question part 2 (OP sutta quote comparing brahmans to dogs)

I see your point, but you're looking at the whole issue from a sectarian worldly frame of ethics. The Buddha is looking at the situation from the point of view, that a true Brahman (in the original non buddhist sense) is supposed to live in a way dictated by their ancient traditions that leads to rebirth in the Brahma realms. That comes from doing lots of brahma vihara practice, and keeping 8 precepts. So the modern Brahmans he's making fun of, they're no better than ordinary non brahman worldlings who make money, have wife and kids, etc. The issue wasn't about the ethical way of having wife and kids, the issue is that brahmans who are supposed to join Brahma, are not going to do so if they can't even follow 8 precepts. And the Buddha uses the satire to point out that even dogs were doing a better job of following ancient Brahman customs than the modern Brahmans. 

(follow up question) What about class equality in mating with others outside of caste?

The point here isn't about whether the latter Brahmans are being less bigoted, racist, misogynistic, open minded by how they view other classes and gender, etc. It's that original Brahmans had high standards they needed to maintain which took discipline and restraint. The latter Brahmans, over time, loosened all the (keeping of) standards to the point that even common dogs were more restrained by comparison. It's not about social justice and whatever other modern issues you could criticize, it's about having standards, and being restrained and disciplined in following them, not just following all the base desires like ordinary humans.    

There are other suttas where the Buddha talks about "what makes a Brahman" is their conduct, not their birth into the Brahman caste, their race, etc, and monks losing rank and social status when they ordain (a former slave has same status as a monk as a former Brahman).