Rabbi Hershel Schachter
V'Kidashto: Preserving our Kedusha
In Parshas Emor the Torah enumerates the women whom a kohein may not marry. The halachah does not permit a kohein to marry a woman who converted, even if her conversion took place before she was three years old. There is a minority opinion among the poskim that a convert, who never had relations with a non-Jew, is only rabbinically forbidden to marry a kohein.
Years ago there was a popular notion among achronim that all kohanei chazakah today (kohanim who can not produce documents to prove their status, and are merely assumed to be kohanim), are only safek-kohanim.
Some put two and two together and came up with the following conclusion: any kohein today, who is only a safek-kohein, may marry a gioret who was converted as an infant, based on the principle that in any instance of a safek in a din derabbonan, we go lekulah (and follow the lenient position).
This position is not correct. First of all, since the days of Rav Akiva Eiger and the Chasam Sofer, the position of Rav Zvi Hirsch Kalischer, that kohanei chazokah are considered vadai Kohanim, has been accepted and as such, they are only rabbinically prohibited from offering the korbanos in the Beis Hamikdosh.
Furthermore, the Talmud, when discussing the prohibition of a kohein marrying a chalutza, states that because the prohibition is only derabonan, if a kohein went ahead and married a woman who is a safek chalutza, b'dieved (after the fact) we would say that they need not get divorced: safek derabonon lekulah. But l'chatchila we would not permit a kohein to go ahead and marry a safek chalutza. (A safek kohein marrying a vadai chalutza is the equivalent of a vadai kohein marrying a safek chalutza.)
The same would be true according to the minority opinion, that a gioret who was converted as an infant (who clearly had never had any relations with a non-Jew), is only rabbinically forbidden from marrying a kohein. We would not permit the safek-kohein to go ahead lchatchila and marry that gioret. However b'dieved, if they already got married, we would apply the rule of safek derabonon lekulah, and the couple would not be required to divorce.
Every so often we have a situation where an observant kohein falls in love with a gioret. An honest bona-fide Orthodox rabbi would encourage that kohein to fall out of love and look for someone else. In recent years there have been some "Orthodox" rabbis who have stood on their heads in order to come up with a "hetter". The latest "work around" ("pattent" in modern Hebrew) runs as follows: a) we know that if a kohein marries a woman whom he was forbidden to marry, his children will be "chalolim"; b) a "cholol" is void of kedushas kehuna and may even marry a divorcee or go to a cemetery; c) a kohein may not marry a woman who was held captive in a non-Jewish prison (technically known as a "shvuya"). Hence it follows (that 2 + 2 = 22) that all children born after the shoah to parents where the father was a kohein and the mother was a "shvuyah" (held prisoner by the Nazis) will be chalalim, and be allowed to marry all psulei kehunah.
This logic, however, is incorrect. a) After WWII the major poskim permitted all those women who were held in prison by the Germans to marry kohanim. They did not consider them shvuyos for various reasons.
b) Even if one were to assume that these women should have the status of "shvuyah", and should not have been allowed to marry kohanim, because the prohibition of shvuyah is only miderabanan (rabbinical), their children would only become chalalim miderabanan. As such they would not be allowed to marry a gerusha or gioret, since that constitutes a Biblical prohibition. Only one who is a chalal on the d'oraysa (Biblical) level is considered totally void of kedushas Kehunah and permitted to marry pesulei kehunah d'oraysa.
c) Even if one were to adopt the minority opinion and assume that the prohibition for a kohein to marry a gioret who converted as an infant is only miderabanan, one should not assume that one who is a chalal miderabanan may marry a woman who is only forbidden to him miderabanan. Poskim discuss whether one who is a ben chalutza (who is only a chalal miderabanan) may marry a chalutza. One might have argued that since that kohein is a chalal miderabanan, and the prohibition against a kohein marrying a chalutza is also only miderabanan, it should be allowed. But most have not adopted this position. One who is a chalal miderabanan, but is still a kohein kasher min haTorah, should still be treated as a kohein, even with respect to marrying a chalutza.
d) Even if one were to assume that the chalal miderabanan should be allowed to marry a chalutza, the child of a shvuya will not be permitted to marry a chalutza! Not all rabbinic prohibitions are on the same level . The prohibition of shvuya is on a lower level of severity than the prohibition of chalutza. Shvuya was initially introduced as a chumra. The son of the shvuya would only be a lower level chalal, and would not be permitted to marry a chalutza (and certainly not a gioret) which is of a higher level of severity.
The Torah commands us specifically to preserve the sanctity of the kohanim. In the opening posuk in Parshas Kedoshim the Torah commands all Jews to act in a fashion of kedusha. Rashi (in his commentary on that posuk) quotes from the medrash that a major aspect of "kedusha" involves refraining from forbidden marriages. Instead of treating the halachic system as a game and always searching for "a hetter", we ought to train ourselves in self-restraint. Rather than trying to impose our desires on the Torah, we must curb our desires to conform to Hashem's will as he expressed it in the Torah. Furthermore, one should not be concerned that by adhering to the laws of the Torah he will become scarred emotionally. "The paths of the Torah are all most pleasant, and all her ways are peaceful."
 Kiddushin (78a-b)
 See Otzar Haposkim, Even HoEzer ( 6:49 )
 Pischei Teshuva to Even HoEzer (6:2)
 See Rav Zvi Hirsch Kalisher's "Drishas Zion". His suggestion was accepted by Rav Akiva Eiger (his rebbe) and the Chasam Sofer (the son in law of Rav Akiva Eiger)
 Yevamos (24a) and Even HoEzer (6). See Otzar Haposkim there (#8)
Shulchan Aruch Even HoEzer (7)
 Teshuvos Chelkas Yaakov (vol. 1, #16); Teshuvos Minchas Yitzchok (vol. 1, #87)
 Teshuvos Chelkas Yoav (Even HoEzer, #35). This topic is known as "mima nafshach derabanan". Rav Yosef Engel dedicated an entire essay to this theme in his sefer Lekach Tov (#13). See also Avnei Nezer Yoreh Deah (vol. 1, #124) where he demonstrates based on a TOsefta that we cannot say mima nafshach on a d'oraysa level.
 See Tosafos, Menachos 31a, s.v. kasavar
 See Otzar Haposkim to Even HoEzer (7:2)
 V'Kidashto - Vayikra (21:8)
 See Avos (2:4), "bateil retzoncha..." Also see the famous comments of the Ibn Ezra (Shemos 20:14 ): the farmer knows he can never marry the king's daughter, so he will never develop a desire for her. One can not develop a desire for something which is clearly out his reach. A relationship that is forbidden by the Torah must be understood to be out of our reach.
 Mishlei (3:17)