Rava
lectured in Mechuza: “A convert is permitted to marry a daughter of a
Kohen.” The people of Mechuza loaded him with fine silks. He then
taught them: “A convert is permitted to marry a woman who is a mamzer.”
They said to him: “You have ruined the effect of the first statement
you made.”
Shetuki (he whose unmarried mother silences him when
asked about the identity of his father) should not marry an Israelite
of unblemished lineage. Even though he is Kosher, since most of the man
who might have been father are Kosher, this is an additional measure to
protect genealogical purity.