They will explain their rationale for speaking boldly by referencing the prophet Jeremiah, frequently viewed as a "prophet of doom" or a prophet of lamentation over the sins of Israel. I really don't have a problem with this approach per se. I certainly sympathize with it. Evil has to be condemned, sometimes with maximum rhetorical force. The Gospel is just as much about the dignity and justice of God (and how He ultimately used that dignity to satisfy that justice) as it is about the dignity of the human person. So when you read this, don't take me as someone who is a liberal squish who is downplaying the need to condemn sin. Yet I think we need to tell the whole story with our jeremiads, and the best place to look for that story would be the Prophet Jeremiah. The best place to start is when God formally makes Jeremiah his chosen voice:
And the Lord put forth his hand, and touched my mouth: and the Lord said to me: Behold I have given my words in thy mouth: Lo, I have set thee this day over the nations, and over the kingdoms, to root up, and pull down, and to waste, and to destroy, and to build, and to plant.I put the final words in boldface for a reason. Jeremiah isn't condemning just for the sake of condemning. His purpose as a prophet was ultimately to strengthen the people of Israel. He condemned evil, but also urged repentance. If one reads the prophet, one finds lengthy discourses on repentance 7 times in just the first ten chapters. He reminds Judah that God is still willing to take them back, and that all of this judgment business will be over if they are willing to do what they once did, and what they once prospered doing. Jeremiah's entire point was that judgment was not a fait accompli. One person turning from their sins could make a difference. God would've spared Sodom & Gomorrah if a percentage likely in the single digits would've been righteous, and certainly the smallest act of repentance would've turned judgement away.
I honestly do not think this aspect exists in our modern jeremiads. There is seldom talk about how to repent, the benefits of said repentance, God's call of mercy, etc. We are told that God's judgement has come upon us, and we basically just have to deal with it. It is all so very Protestant. The Catholic Church stresses the importance of faithful Catholics doing penance in situations like these. The prayer of the righteous man availeth much. (James 5:16) There is always an extra penance to do, an extra mortification to engage in, an extra prayer or devotion to practice at night. Such might not stop coming judgement, but it can save your soul and that of those around you.
That final point is the most important. Indeed, I believe it is the point by which you should scrutinize all the wannabe Jeremiah's of today, thundering against this or that evil. What steps do they outline for you to avoid the sins mentioned? What concrete advice is given on how to raise your family seperate from these errors even if you must be a part of that wicked society? In the book of Jeremiah, God praises an obscure people known as the Rechabites (Jer 35), whose fidelity to their customs and truths (as they saw them) kept them preserved from what they perceived to be the wickedness of society. That's our goal (to remain preserved from the stain of the world), not that of self-congratulation at how bad things are for others.
As I said earlier, being the "prophet of doom" is a necessary task. Yet we need to remember that the original point of being a prophet is to offer the comfort of God's mercy to the people. I think we need to ask ourselves at every opportunity if we are actually doing this, or just condemning for self-cathartic purposes.