That's a brash statement. He may be controversial and an outspoken askin for the wrong things but nonetheless, what have you seen or heard him do in serious opposition of halacha that makes you publicly out him like that
He cavorts with his female classmates at Columbia, publicly. There are pictures of him hugging and being hugged by females who are not his wife, daughter, mother, etc. I dont know if that qualifies as "serious opposition of halacha", but no purported rabbinic figure that I know of does that.