It appears to me that in Matthew 7:21-23 Christ is speaking of Judgment Day. So you can’t really say that’s pre-grace, if you can see my point.
Agreed there’s no such thing as a “works” salvation (Eph. 2:8-9). We’re saved by the grace of God.
The problem with homosexuality is that the Holy Spirit in Romans 1 declares that its practitioners are turned over to a reprobate mind. That’s a worthless, non-functioning mind that’s essentially spiritually insane.
In fact, Christ also spoke of “dogs” and “swine” just a little earlier in Matthew 7:
Mat 7:6 Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you.
It’s obvious He wasn’t speaking of the four-footed critters. “Swine” is easy. That’s anybody who insists on wallowing in his or her filth. “Dogs” is referring to homosexuals, as mentioned earlier. Once we know either of them for what they are, Christ commanded us to refrain from evangelizing them, because they tend to be turned over to a reprobate mind and tend to get violent when confronted with their sin, however gently.
I am not sure the term “dogs” always refers to homosexuals, although I have mentioned in posts above where it obviously does. But remember the discussion between Jesus and the Canaanite woman where he talked about not throwing bread to dogs, which I suspect was a Jewish saying of the time. There He appeared to be referring to Gentiles. But Jews at that time often also referred to Romans or Greeks as “dogs,” because they considered them unclean (a Jew would not enter their house for example, see Acts 11) and many engaged in homosexual activity because it was approved of in the pagan Graeco-Roman culture. Why “dogs”? Because of the posture of dogs when they have sexual relations, similar to homosexuals.