ehemiah may have been the cupbearer for the king of Persia, but his time in the royal court had by no means turned him into a sissy. This man of God was full of fire & brimstone. Perhaps there has never been a minister of God who was as bold against evil as Nehemiah. Find another preacher who punched members of his audience & pulled their hair out while he was preaching. Nehemiah did that (Nehemiah 13:25). And, that wasn't the only hard stance that he took. He had one man evicted from his quarters.
This chapter really fits very well with Ezra 9 & 10 and sheds good light on the surprising strategy that Ezra and Shechaniah employed in the purification of the people. Obviously, the purity of the Jewish bloodline and the religious loyalty of the people to Jehovah were of the utmost importance during the days Ezra and Nehemiah. And, why not; as they read from "the book of Moses" they deduced that this matter was paramount for them. So, whether the danger was in the friendships that had developed between the true people of God and heathen of the land, or in the marriages which had also occurred between the 2 groups; Nehemiah was determined to stamp it out.
You and I might recoil a bit as we read of Nehemiah's tactics. Yet, even Jesus resorted to physical force when he cleansed the temple of moneychangers (Luke 19:45-46).