Then the Spirit of YHWH came upon Jephthah, and he passed over Gilead, and Manasseh, and passed over Mizpeh of Gilead, and from Mizpeh of Gilead he passed over unto the children of Ammon.
Judges 11:29

There is a time and place for men who are prone to violence. Such men in leadership during times of peace can be a disaster, but when conflict comes, we'd better hope they're still around and willing to take the reins.

Jephthah was a violent fool, but the Spirit of God was still on him, and he was chosen by God to judge Israel. Perfection among mortal men is a fantasy. Don't expect too much and don't confuse unpleasantness with incompetence or even inappropriateness. Sometimes rudeness and even violence is exactly what we need.