I have two answers to the op:
1. Two people can ask the exact same question but be asking entirely different questions. In other words, the words may be the same but they are coming from two entirely different places, and a good mechanech understands what the person’s real question really is.
My mother is bt and one of the main hashpaos on her (both for becoming Frum and for making aliyah) was her 7th grade sunday school teacher. She happened to see him at the Kosel several years ago, and he was shocked to discover that she had become Frum and made aliya. She asked him why he was surprised, and he said, “because you used to ask so many questions.”. She was like, “Why do you think I was asking questions?”
The moral of the story is that sometimes someone could be asking questions in a way that sounds like the Rasha in the Haggadah but that isn’t really where they are coming from. Many of today’s at-risk kids could be asking questions that sound like attacks but are really coming from a place of pain and confusion and a desire to be part of things (as opposed to the Rasha who did not want to be part of things).
The Rasha was deliberately attacking. He had nothing in common with most kids at risk of today. The words may sound the same, but they are coming from a completely different place. Before you can decide how to respond to each son, you have to know which son he is. You can only do that if you look into his heart, into what is behind his words, and not merely the words themselves. (I don’t have a Hagadda in front of me, but don’t two of the sons actually use the same words?)
Answer #2: Sometimes, there are people who need a sharp response. That doesn’t take away from the “ahavas chinam”. Being sharp or strict does not have to be a contradiction to love. I knew a girl who was learning in a certain program in Israel. She was from a modern background and had a strong personality and used to phrase her questions/statements in ways that were less than appropriate. Her teacher/head of the program understood that she was someone who needed a “hakheh es shinav” approach. This was despite (or perhaps because of) the fact that she really was sincere.
He understood that this was the approach that she needed (because of the way she expressed herself) and that this is what would work for her. And he was right. She very much appreciated his approach and she grew from it, and at the end of the year, he was the teacher whom she had the hardest time saying goodbye to.
Point #3: I think that the difference between today and the time when the Hagadda was written is that today most people are very emotionally fragile and that’s why for many people today, the strong approach doesn’t work.
But that doesn’t mean c”v that the Torah changed and that what it says in the Hagada doesn’t apply today. Then and now, there were different types of people who needed different responses. Today, there may be less people who need the strong approach, but there is still a place for it, if one knows when and how to do it.
For example, many people do use it when dealing with adult political leaders who are trying to uproot the Torah, and it seems to me that at least in some of those cases, it is the right approach.