Regarding A: I do not know the passage well enough, but doesn’t the Rabbi accept the view of Nimukei Yosef, brought by the Kesef Mishneh in Laws of the Foundations of the Torah chapter 5, that a Jew who has relations with a non-Jewish woman falls under the category of severe forbidden sexual relations, because “there are times when he incurs death on account of her, since zealots may strike him, and if they did not strike him he is liable to karet”?
The Hagahot Maimoniyot there, note 2, also implies that only a Jewish woman who had relations with a non-Jewish man is not included among forbidden sexual relations.

And what they wrote about Joseph the righteous and Potiphar’s wife—that the dog would be tied to him in the World to Come. From the standpoint of Kabbalah, is that not severe?

That is only in public, or in the context of marriage (according to the view that the prohibition of intermarriage is not only with the seven nations). In private it is permitted on the Torah level, until the religious court of the Hasmonean house came and decreed against non-Jewish women because of נשג״ז.

Y.D.,

The Kesef Mishneh in chapter 5 of Laws of the Foundations of the Torah wrote, according to the view of Maimonides and Nachmanides, regarding a Jewish woman who had relations with a non-Jew, that this is not forbidden sexual relations, because if it is in a promiscuous context it is from the decree of the court of Shem, and if in marriage it derives from “you shall not intermarry with them.” But I understood that this is specifically about a Jewish woman, because afterward he brought the words of Nimukei Yosef that I cited earlier.

We should institute an ordinance by the sages of this generation that people may marry only a non-Jew/non-Jewess, and that way we’ll save many sins?!??!?!

Obviously marriage with a non-Jewish woman is much more severe, and that is why in public zealots may strike him, something not said regarding any prohibition other than stealing Temple vessels. The formal halakhic punishment is more severe when we are discussing a one-time act, and this requires further analysis.

Besides that, the Rabbi did not pay attention to additional transgressions that result from marrying a non-Jewish woman, and seemingly one may even desecrate the Sabbath to prevent such marriages, just as one may in order to prevent apostasy, unlike the case of a non-Jewish woman.

And furthermore, is the only measure of a prohibition’s severity its punishment?

Rabbi Akiva,
I see no source for this karet, and the rule that zealots may strike him is not an indication of anything on the halakhic level.

Ezra,
you’re giving homiletics here. That’s nice for the upcoming kiddush in synagogue. Jewish law has its own reasoning, and it is not very impressed by homiletics.
Beyond that, it’s worth reading the discussion before responding. We were talking about intercourse without marriage/children.
You decided that the measure of the prohibition’s severity is the punishment, and you also decided that the rule that zealots may strike him is a punishment. On the first point, that may be some kind of measure, but certainly not the only one. On the second, you simply made a mistake.

According to Maimonides, a Jew who has relations with a non-Jewish woman in private is punished with karet by words of the Prophets.
There is a responsum about this in Yabia Omer, part 6, Choshen Mishpat, siman 3.

And therefore?

Sorry,
I wrote that because you wrote to Rabbi Akiva that “you see no source for this karet.” The source is from the Prophets.

Michi, you wrote to Ezra, “…you decided that the rule that zealots may strike him is a punishment, etc.—you simply made a mistake.”
Do you mean that this rule is in the category of permission for zealots and not a punishment for the transgressor? If so, isn’t that true of all death penalties as well?
Stoning is not a punishment for one who publicly desecrates the Sabbath, but rather permission for the Sanhedrin to kill him.
Thank you.

It is more than permission. It implies that it is proper for zealots to do so. In court-imposed death penalties, it is an obligation on the religious court to do so.