It is for Sanhedrin to judge him, but they usually can’t. Where did you see Rachavam being referred to as a Rasha?
If you think there is intermarriage when it is easy to be a Frum Yid, do you think it will happen less when people the desire to be like the outside will have physical reallity?
By the way, besides for Kehuna and Melucha, Srara is supposed to be through votes. Chazal say that although Hashem chose Betzalel to be in charge of the Avodas Hamishkan, He told Moshe Rabbeinu to get the votes of the people.