Commentary for Kiddushin 25:12
הדר יתבי וקאמרי הא דאמר רב יהודה אמר שמואל כל שאינו יודע בטיב גיטין וקדושין לא יהא לו עסק עמהן אמר ר' אסי אמר רבי יוחנן וקשין לעולם יותר מדור המבול שנאמר (הושע ד, ב) אלה וכחש ורצוח וגנוב ונאוף פרצו ודמים בדמים נגעו
Said one of the Rabbis, R'Jacob by name, to them: Thus did R'Assi say in R'Mani's name: Just as a woman cannot be acquired by less than a perutah's worth, so can real estate not be acquired with less than a perutah's worth. But, they protested to him, it was taught: Although a woman cannot be acquired for less than a perutah's worth, land can be acquired for less than a perutah's worth? - That was taught only in respect to barter, he answered them. For it was taught: Acquisition can be effected through an article, even if it is not worth a perutah.<span class="x" onmousemove="('comment',' Barter (Heb. halifin) is a system of symbolic exchange, the article with which it is effected symbolically representing the larger article or the money which is actually the purchase price: consequently it may be worth less than a perutah. But when acquisition is effected through money itself, or an article valued as money, what is not worth a perutah does not rank as such.');"><sup>13</sup></span>
Daf Shevui to Kiddushin
R. Joseph interprets this in reference to those who bring forth illegitimate children through adultery. Improper adjudication of matters of divorce and betrothal can also cause illegitimate children to be born. This “adds sins to sins” for not only was the original intercourse sinful, these children will be mamzerim and when they marry into Israel, this too will be in sin (according to rabbinic understanding).
R. Assi posits that this sin is worse than the sin of the generation of the flood for in the verse in Hosea even the fish die, whereas in the flood they did not.