(2) One does not make a עיר הנידחת [city that worships idols and thus must be destroyed.] of a city that is on the border of Israel. The Rambam brings the reason so as to not let the enemies of Israel have an entry point into Israel. That is the reason of R. Shimon ben Yochai that we are דורשים טעמה דקרא. [The sages say the reason is the verse that says בקרביך in your midst.]
The answer is given that there is not difference in law so the Rambam does always prefer to bring a verse than a drasha.
The Minchas Chinuch asks --but in this case there are many difference in law.
Rav Shach says once the law does not apply in the opinion of R. Shimon then the city no longer has the category of עיר הנידחת. First I want to bring a proof for Rav Shach since in the opposite kinds of cases where there is a prohibition we do not say that in the opinion of R. Shimon the prohibition remains in effect but there is a special exception in case the reason does not apply.
Another question is that the Rambam usually brings a verse as a proof of a law rather than some reasoning process. Here he does just the opposite. It seems to me he is specially going like R Shimon here like he does in Yevamot where he prohibits to marry any woman that serves idols, even if she is not from the seven Canaanite nations -which is the law of R Shimon, not the sages.
(3) In Genesis God says the reason gentiles are forbidden to murder is because בצלם אלהים עשה את האדם. Therefore we have an open verse telling us that gentiles are made in the image of God [as per the Rambam]
(4) King Oshiyahu that in his days the Torah scroll was found in the Temple sent to Chulda the prophetess who said the punish that was decreed was because the Jewish people were not obeying the commands of God. Therefore the laws of the Torah must have been known even before the scroll was found.
(5) The King of Sodom said to Avraham תן לי הנפש והרכוש קח לך the Satan says to a man "give me your soul and take the money" [That was my first "vort" after I got to yeshivat Shar Yashuv in NY]
(6) One of the arguments that Job had with his friends involved time. One friend said the wicked are punished very soon after they sin. Job said they live all their days in peace and happiness and abundance. The question seems to me to be not if there is punishment for sin but rather is there in this world a connection between crime and punishment?
(7) King Yoshiyahu also found some graves an spread the bones over the altars of the idol worshippers to make them "tame" unclean. He obviously did not have any religious people around trying to stop him like they do in Israel. I even brought this up with a person in Israel who really did know how to learn. I showed him the law in the Rambam that it is allowed to move graves for building roads. This was right at the time the insane religious people were trying to stop some building project as is their general custom to stop every good thing. One thing I noticed about the religious. They love bones. And they ruin the whole project of Torah. By pretending to keep it, they ruin it for everyone, and make it odious in people' eyes by their disgusting actions and character. How this happened I do not know but but their pretense of righteous is a horrific scam. I avoid them. The only place I would learn and pray at would be a Litvak yehiva that excludes all the garbage.