We all always desire to be called and addressed respectfully, no one would like to be presented as a bad person, even if that be the reality of our life.
"Then he said to the multitudes that came out to be baptized by him, “Brood of vipers! Who warned you to flee from the wrath to come?" Luke 3:7 (NKJV)
John the Baptist was a prophet sent by God and seeing the multitude of people he addressed them as 'Brood of vipers", for John did not see the world as a worldly man, rather he saw it from the eyes of the Lord.
Being a child of God we should react and see things as God would have seen them, for Paul clearly says...
"For “who has known the mind of the LORD that he may instruct Him?” But we have the mind of Christ." 1 Corinthians 2:16 (NKJV)
for only when we see things, situations and people as God sees them, we would see them rightly and perfectly.
The world was in a chaos as John the Baptist saw it and thus he powerfully preached the Word of God, how do you see the world today?
Do you also not see the world and the people as living in sin, away from God, lost in the material blessings, not believing in God and always desiring to be in sin?
Thus, there is a great need to preach the Word, for even though the people address each other much respectfully even today, the real picture may still be 'brood of vipers' who need to come to God.