Deuteronomy:17:1 – You shall not sacrifice to the Lord, your God, an ox or a sheep that has in it a blemish or any bad thing, for that is an abomination to the Lord, your God.
Sifri: We learn in a beraisa that Rabbi Shimon said: One might think that just as an ox or a sheep become invalid for being used as a sacrifice if it was used for immoral sexual relations, so too a Cohen would become invalid. However, since the verse states “it is an abomination to the Lord” we see that the animal becomes invalid but not a Cohen.
Coloquial translation of Note 6:
See also the Mishna in Bechoros (7:7) where it lists reasons why an animal would become invalid yet would not apply to a Cohen. In the list, it includes animals that were used for sexual immorality and also animals that killed a person. The Tosfot Yom Tov states that in some editions of the Mishna it excludes the phrase “that were used for sexual immorality and also that killed a person”. The Tosfot Yom Tov states this because of what it says in the Gemora Bechoros (32a) that Rabbi Yochanan states that a Cohen who has killed someone is forbidden to participate in the communal blessing ceremony. A logical deduction would be that he is also forbidden from participating in the service in the temple when it was standing. This is also true of a Cohen who committed sexually immoral acts.
However, the Sifri explicitly disproves his comments. The Sifri state that a Cohen who commits sexually immoral acts would still be allowed to participate in the communal blessing ceremony. Further, the Tosfot Yom Tov’s observation that it would be a logical deduction to ban such a Cohen from the temple service would only be a [optional] stringency not the strict letter of the law.
In Numbers (6:27) regarding the verse “and I will bless them”, I show that the Jerusalem Talmud Gittin (5:8) explicitly states that a Cohen who has committed sexually immoral acts or who has killed someone is permitted to participate in the communal blessing ceremony.
Translator’s Note: Not only does the Torah Temimah mention his view on this once, he mentions it twice; once in Numbers (6:27) and once here. I think this indicates that he feels very strongly about this issue.