I know Jesus had used some strong language to certain leaders but also he showed gentleness and healing in his words. What is the good balance in showing gentleness in our words but also boldness and frankness when necessary?
There is a difference between being bold and frank concerning the scriptures compared to language that is devoid of grace.
Imagine if you will and recall the parables Jesus delivered to those who sought to query Him about His eternal message. "What must I do to be saved?"
What of that if Jesus had responded with insults toward that person making the inquiry, made fun of their inability to understand what He was certain He made clear prior.
To make it a broader picture, imagine when you have read someone displaying a lack of grace and respect for someone, and those words they publish for the world of the web to read and judge as to what that display affords the image and character of a Christian. Now in re-reading such a post, picture Jesus speaking those same words to any of those persons whom He ministered to.
What do the scriptures teach about ad hominem attacks, hate, mockery, ridicule. Were any of those sinful behaviors exampled by Christ? Even when He confronted the Pharisee? Jesus didn't use the methods we encounter in forums from verbally offensive persons. Jesus in His rebuke used terminology that painted a picture, a parable in its own right, as to the character of those whom He judged. He spoke to the Pharisee's, the ministers of the law, in such a way as they understood; vipers, synagogue of Satan, etc... Because those symbols were in the Torah so as to deliver those messages to the people concerning those behaviors, and allegiances.
Those who for the most part are never kind and rarely demonstrate the grace of God using Christ as the excuse or role model for their behavior are of course wrong. Tantamount to saying, Jesus acted the same way and I'm just using His example to defend His truth. What would Jesus say to that?
The Book of Matthew chapter 5 (The Sermon on the Mount)
21 “You have heard that it was said to those of old, ‘You shall not murder; and whoever murders will be liable to judgment.’ 22 But I say to you that everyone who is angry with his brother[
c] will be liable to judgment; whoever insults[
d] his brother will be liable to the council; and whoever says, ‘You fool!’ will be liable to the hell[
e] of fire. 23 So if you are offering your gift at the altar and there remember that your brother has something against you, 24 leave your gift there before the altar and go. First be reconciled to your brother, and then come and offer your gift. 25 Come to terms quickly with your accuser while you are going with him to court, lest your accuser hand you over to the judge, and the judge to the guard, and you be put in prison. 26 Truly, I say to you, you will never get out until you have paid the last penny.[
f]
The Book of Proverbs chapter 15:1 A soft answer turns away wrath, but a harsh word stirs up anger.
Hateful words encourage hateful responses which goad the initial offender to continue on that path. In truth, the initial offender does not lead anyone to know the truth using such tactics. Rather, their behavior extends an invitation for their target, if they're so inclined, to respond in kind.
How many people come to Christ immediately after being verbally abused by a Christian?
Verbal Abuse: A Biblical Perspective
The Book of 1st Peter chapter 3
15. But in your hearts honor Christ the Lord as holy, always being prepared to make a defense to anyone who asks you for a reason for the hope that is in you; yet do it with gentleness and respect,
1
Thank you. 
