“So I reprimanded them and called down a curse on them and struck some of the men and pulled out their hair and made them swear by God: ‘You should not give your daughters to their sons, and you should not accept any of their daughters for your sons or yourselves.'”
~Nehemiah 13:25

Was Nehemiah’s reprimand toward the Jewish men who had married pagan women a cruel overreaction?
To answer this question, let’s look at other Bible passages that warned the Jews against this practice.
“But if you […] form marriage alliances with them […] They will become a trap and a snare and a scourge on your flanks and thorns in your eyes until you have perished from this good land […]”(Josh. 23:12,13).
“For they will turn your sons away from following me to serve other gods; then Jehovah’s anger will blaze against you, and he will swiftly annihilate you.”(De. 7:4).
Because the Jews could not count on God’s protecting them as a People if they married pagan women, obedience to this particular mandate was a matter of life or death.
It implied the survival of the nation to which the Messiah would eventually be born (Luke 12:48).
This is why Nehemiah deemed it necessary to urgently carry out a form of discipline common to their day: corporal punishment.
“If the wicked one deserves to be beaten, the judge will have him lie down prostrate, and he will be beaten in his presence. The number of strokes should correspond to the wickedness of his deed,” (De. 25:2).
“Bruises and wounds purge away evil, and beatings cleanse one’s innermost being,” (Prov. 20:30).
“And everyone who does not observe the Law of your God and the law of the king should have judgment executed on him promptly, whether it is death, banishment, a fine, or imprisonment,” (Ezra 7:26).
Though this is definitely not an exercise in supporting corporal punishment toward one’s neighbor, one can understand how Nehemiah’s actions as governor of the Jews would not have been seen as extreme as a reader may find them today.
Jehovah promptly corrected His People through Nehemiah because he loved them (Heb. 12:6).
Their lifestyle would have otherwise brought about His disapproval and as a result, their own annihilation.