Comentario citado sobre Deuteronómio 23:3

ולא יגלה כנף אביו AND HE SHALL NOT UNCOVER HIS FATHER’S SKIRT — This refers to the שומרת יבם of his father (the widow of his father’s brother who died without issue, and who is waiting (שומרת) for her brother-in-law (יבם) either to marry her or to put her through the ceremony of release, חליצה), who is thus destined for his father. But has he not already been prohibited about her (i.e. forbidden to marry her) on account of the law (Leviticus 18:14) “the nakedness of thy father’s brother [thou shalt not uncover]”?! But the prohibition is repeated here in order to make him transgress two negative commands if he takes her (Yevamot 4a), and in order to put into juxtaposition to it the law (v. 2) “one born of incest or adultery (ממזר) shall not come [into the assembly of the Lord]”, and thereby to teach that one is termed ממזר only if he is born from those liable to the penalty of excision on account of the intercourse between them, as is the case with one who take’s his father’s שומרת יבם, who is forbidden to him under the penalty of כרת as אשת אחי אביו; cf. Leviticus 18:14 and Leviticus 18:29 (but not if he was born of a woman intercourse with whom involves only flagellation), and it logically follows that the term applies also to one born from those liable to one of the death penalties by sentence of the court, for amongst the cases of forbidden intercourse there is none punishable with death by the sentence of the court which does not involve the penalty of excision (if it was not preceded by a warning) (Yevamot 49a; cf. also Rashi on Kiddushin 67b s. v. מהנ״מ).

An Israelite who marries a mamzereth or natinah, or an Israelite woman who is married to a mamzer or a natin. This section lists marriages forbidden to ordinary Israelites. A mamzer or mamzereth (a female mamzer), mentioned in Deuteronomy 23:3, is one born of a forbidden union which carries with it a punishment of kareth or death. A natin or natina (a female natin) is a descendent of the Gibeonites, those who tricked Joshua into accepting them as converts, upon which he declared them to be woodchoppers and water-drawers and forbade them to marry ordinary Israelites (Joshua 9:27).

Rabbi Judah forbids it. Seemingly Rabbi Judah says that every person from a class forbidden to enter into the assembly must marry another person from the same class. A mamzer would have to marry a mamzer, a shtuki would marry a shtuki, etc. The problem with this interpretation of his words is that there is no inherent logic to it. The Talmud explains that Rabbi Judah prohibits converts from marrying mamzerim. The Torah states that a mamzer should not come into the assembly of the Lord (Deuteronomy 23:3). The question is: are converts considered part of the “assembly of the Lord”? According to Rabbi Judah the convert is part of the assembly of the Lord, and therefore they cannot marry mamzerim.