People malign Manu without studying his work in full.
Texts are often taken out of context to suit one’s convenience.
Whatever be the subject, deep thought seems to have gone into and these Laws are arrived at after taking into consideration the stability of the Society and the welfare of the individual.
However Social Order seems to take priority.
The Laws of Manu on selecting a Bride , to me, seems very rational.
As parents most of us follow the same without articulating or even aware of it.
To ensure Offspring without Genetic disorders Manu prohibits marriage with immediate blood relatives.
And with chronic illness and birth defects.
He insists on not marrying from a Family without a Male Heir.
Boys’ parents know how difficult it is to interact with a child with no brother/s for they normally are unaware of Mael view-point.
And in the event of the demise of the girl’s father, if there are no Males to interact on behalf of the Girl, it creates n running the Family at times of crisis.
Manu pays scant regard to the wealth of the Girl’s Family.
He has also provided some physical marks which might have a bearing on the character of the Bride.
Some of his observations are vindicated by Science, like the one regarding excessive Body hair-normally the extra hair growth is because of imbalance in Hormones.
Read the Laws of Manu on this.
Though this appears to apply for Brahmins, my view is that these laws are meant for the three Varnas, Brahmana, Kshatriyas,an Vaisyas as Manu simply lays down these rules for the Dwijas(twice Born)
That is those who wear Upaveeda.
These three varnas must wear Upaveedas.
Therefore these rules of Manu apply to all the three castes.
4. Having bathed, with the permission of his teacher, and performed according to the rule the Samavartana (the rite on returning home), a twice-born man shall marry a wife of equal caste who is endowed with auspicious (bodily) marks.
5. A damsel who is neither a Sapinda on the mother’s side, nor belongs to the same family on the father’s side, is recommended to twice-born men for wedlock and conjugal union.
6. In connecting himself with a wife, let him carefully avoid the ten following families, be they ever so great, or rich in kind, horses, sheep, grain, or (other) property,
7. (Viz.) one which neglects the sacred rites, one in which no male children (are born), one in which the Veda is not studied, one (the members of) which have thick hair on the body, those which are subject to hemorrhoids, phthisis, weakness of digestion, epilepsy, or white or black leprosy.
8. Let him not marry a maiden (with) reddish (hair), nor one who has a redundant member, nor one who is sickly, nor one either with no hair (on the body) or too much, nor one who is garrulous or has red (eyes),
9. Nor one named after a constellation, a tree, or a river, nor one bearing the name of a low caste, or of a mountain, nor one named after a bird, a snake, or a slave, nor one whose name inspires terror.
10. Let him wed a female free from bodily defects, who has an agreeable name, the (graceful) gait of a Hamsa or of an elephant, a moderate (quantity of) hair on the body and on the head, small teeth, and soft limbs
Laws of Manu Chapter III .