In the Rashi, the writer is explaining what kind of taunting is forbidden when dealing with a ger (at issue is the type of "tonu" which assumes that "ger" is a religious convert. There is no "for instance" -- the brackets indicate that this is inserted by the editor of the English translation. Try this translation
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This implies vexing him with words (cf.
Rashi on Exodus 22:20) — do not say to him, “Yesterday you were an idolator and now you come to study the Torah which was given from the mouth of the Almighty!” (Sifra, Kedoshim, Chapter 8 2;
Bava Metzia 58b, 59b.)
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The Chizkuni on Ex 22:20 writes
וגר לו תונה, “and you must not oppress a convert;” the reason why this verse follows that about converts serving both Hashem and their previous deities, is that G-d wishes to go on record that although He finds serving another deity as something repulsive, He does love converts and appreciates that they distanced themselves from their former religion.
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The Rabbeinu Bahya and the Ralbag on that verse are also pretty explicit. The Rashbam writes (on Ex 20:22)
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, do not wrong him with words. In
Leviticus 25,14 the Torah refers to similar legislation when applying to monetary matters. The same legislation applies to not wronging fellow Jews who are not converts, of course. The reason the Torah chose the convert as the example of the victim in our verse is that converts have much less of a chance to protect themselves against abuse of any kind, seeing they have no family to stand up for them if a wrong has been committed against them. Not only this, it is so easy to wrong a convert by mentioning what his parents do and what he himself used to do before he converted.
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The Tur Ha'aroch, referencing the Ramban writes
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I think that the moral/ethical message here is that we must not taunt the proselyte, reminding him of his lack of illustrious ancestors, seeing that we ourselves not so long ago were no better than he while we were idol worshipping aliens in Egypt. I, the Lord, have saved you from there because I took note of your pitiful state. Similarly, any proselyte will certainly also enjoy My full protection a soon as he turns to Me complaining about being discriminated against.
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So, again, how are these rabbinic voices NOT talking about specifically religious converts?