was learning with my chavrusa last nite in mesechta rosh hashana and the gemara was talking about 'poshei yisrael bigufan' and poshei umos ha'olam bigufan'. the gemara explains poshei yisrael bigufan to mean karkafta d'lo manach tefilin, a skull that does not wear tefilin, while poshei umos ha'olam means ba'aveirah, which the rishonim explain to be referring to z'nus. i asked my chavrusa what would a yisrael who is ch'v oiver on z'nus be considered? why only the goy who does it is considered a posheiya bigufan? he answered that if and when a yid does something like that he does not enjoy it fully, he has that little voice in the back of his mind saying "yankel, you should know better that to get involved in something like this". as opposed to the goy who can put on his gartel and make a leshem yichud to do whatever he wants and have no qualms about it.
Rav Shraga feivel Mendlowitz z'l used to give a shiur in sefer Tanya to his bochurim in Torah Vodaas. once, after learning a particularly deep inyan he said "i don't know if what we just learned can be practically fulfilled by all of you, but one thing i can be sure of is that you cannot enjoy an aveirah fully after learning this".
They say that the Bardichever zy'a said once "look Ribono shel olam how yidden will spend so much money to buy the best food for shabbos and yomtov and for a wedding, a bar mitzvah, a siyum, a bris, whenever there is a festive occasion they pull out all the plugs to get the best of everything. did you EVER hear of a yid making a party to celebrate after he did a really 'good' aveira?"
after the fact it is never enjoyable. it is a temporary blindness, a ruach shtuss.